The Disposal of the Sewage of the Sanitary District of Chicago

A K o]')0]i f o the DktHei Engbeer,

U- Erifkofer- Office, Ghita^o

—

DATE DUE

ISWS Aivoru, Duruit/K oc nvwov^xi THE B THE DISPOSAL OF THE 23 SEWAGE OF DISTRICT OF Loan c. 1 SANITARY 05041003 CHICAGO.

ILLIHOlSSTi^T

ISWS Alvord, Burdick & Howson B THE DISPOSAL OF THE 23 SEWAGE OF THE Loan SANITARY DISTRICT OF

c. I CHICAGO. 05041003

pEMCO / STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION

DIVISION OF THE STATE WATER SURVEY A. M. BUSWELL, Chief

BULLETIN NO. 23

THE DISPOSAL OF THE SEWAGE OF THE SANITARY DISTRICT OF CHICAGO

A Report to the District Engineer

U. S. Engineer Office, Chicago BY ALVORD, BURDICK & HOWSON, Engineers

[Printed by authority of the State of Illinois]

URBANA, ILLINOIS

CONTENTS

Page

Organization , iv. Letter of transmittal v. Letter of authorization vi.

Part I. —Introduction, summary and conclusions 1 Part II. —Present disposal of sewage and deficiencies 12 Part III. —Population and growth 39 Part IV. —Amount and quality of sewage 48 Part V. —Standard of maximum pollution 64 Part VI. —Required degree of purification with various dilutions. 79 Part VII. —Protection of the water supply 85 Part VIII.—Savings effected by metering 101 Part IX. —Volume of sewage 114 Part X. -—Future intercepting sewer construction 119 Part XI. —Methods of sewage disposal and practicable efficiencies 128 Part XII. —Sewage disposal costs in other cities 145 Part XIII.—Required works for 10,000 cubic feet per second flow. 170 Part XIV.—Required works with 4,167 cubic feet per second flow. 174 Part XV. —Required works with miscellaneous flows 180 Part XVI.—Review of expenditures under various flows 185

PHILLIPS BROS.- PRINT. SPRINGFIELD. ILLINOIS.

°2 1 9 7 (60418—1500)

iii. ORGANIZATION.

STATE OF ILLINOIS

Len Small, Governor

DEPARTMENT OF REGISTRATION AND EDUCATION

A. M. Shelton, Director

Board of Natural Resources and Conservation Advisers

A. M. Shelton, Chairman

William A. Noyes, Chemistry, Henry C. Cowles, Forestry. Secretary. William Trelease, Biology. John W. Alvord, Engineering. C. M. Thompson, Representing the Edson S. Bastin, Geology. President of the University of Illi- nois.

Water Survey Division Committee

A. M. Shelton William A. Noyes C. M. Thompson John W. Alvord

WATER SURVEY DIVISION

A. M. Buswt:ll, GTiief

iv. LETTER OF TRANSMITTAL.

State Water Survey Division

ARTHUR M. BUSWELL, CHIEF

Urbana, III.

February 18, 1927.

A. M. Shelton, Chairman, and Members of the Board of Natural Resources and Conservation Advisors:

Gentlemen : Herewith I submit a report on the disposal of the sewage of the Sanitary District of Chicago and recommend that it be published as Bulletin No. 23 of the State Water Survey Division. This report was prepared by Alvord, Burdick & Howson, consult- ing engineers, of Chicago, by order of the Secretary of War pursuant to a resolution of the Committee on Rivers and Harbors of the House of Representatives, U. S., April 14th, 1924, and submitted to the Dis- trict Engineer, U. S. Engineer Office, Chicago. The printing of this report as a Water Survey Division Bulletin has been authorized by the Secretary of War. The letter granting this authorization is included herewith. The material presented in this manuscript contains so much data on the cause and remedy of the most serious stream pollution problem in the State that it seems highly advisable to make it available to the citizens of the State in published form. Respectfully submitted, A. M. BusWELL, Chief.

V. LETTER OF AUTHORIZATION.

War Department

United States Engineer Office

537 South Dearborn Street

Chicago, Illinois

October 25, 1926.

Dr. A. M. Buszvelly Chief, State Water Survey Division, Board of Natural Resources and Conservation, Urbana, Illinois,

Dear vSir : Your request for permission for the State Department of Registration and Education to print the report of Alvord, Burdick & Howson, Engineers, to the U. S. District Engineer on the Disposal of the Sewage of the Sanitary District of Chicago, has been approved by the Chief of Engineers, with the condition that Chapter XII be also published, and that credijt and acknowledgment be made to the Chief of Engineers and the War Department, for whom and under whom the report was prepared. Yours very truly, Edward H. Schulz, Colonel, Corps of Engineers, District Engineer.

vi. : ;

PART I.

INTRODUCTION, SUMMARY, AND CONCLUSIONS.

District Engineer,

U. S. Engineer Office, 337 S. Dearborn St.,

Chicago, 111. Dear Sir:

Proceeding under our instructions of January 16, 1925, we have studied the problem of sewage disposal for the City of Chicago and vicinity, including more particularly that territory embraced within the Sanitary District of Chicago. Our study has been particularly directed to answers for the following questions (a) Determination of a pollution standard for the Chicago Drain- age Canal for each of the following average diversions from Lake Michigan and 10,000 cubic feet per ; —2,000, 4,167, 6,000, 7,500, 8,500 second ; this standard to be the lowest that will prevent the occurrence of nuisance in the Des Plaines and the Illinois River, and will permit a thriving fish life therein. These diversions include the sewage flow of the Sanitary District and they therefore represent the dry weather flow of the Drainage Canal at Lockport, approximately. (b) Determination of the extent to which purification measures must be taken by the Sanitary District of Chicago for each of the flows specified above, in order that the pollution standard be maintained unim- paired. (c) Determination of the most feasible method of treating the surplus pollution, and, for each flow specified, the cost of the necessary works and the operating costs thereof. (d) The determination of the time that reasonably would be required to build the necessary works and place them in operation for each of the flows specified. In the study of this matter the time at our disposal has not permitted original investigations. It has been possible only to view the present situation by inspection, and to study the large amount of data that has been accumulated by the Sanitary District of Chicago and . other agencies, bearing directly upon the answers to the above questions. :

We have further brought to bear upon the study of the problem the experience of other cities regarding sewage disposal, insofar as information has been gained that would throw light upon the Chicago situation. Upon the pages which follow we have stated the local problem in

some detail, and we have discussed the various phases of it insofar as we believe is required for a general understanding of the problem, and our answers to the questions previously stated. For the benefit of those already somewhat familiar with this problem we will first briefly state our summarized findings and conclusions. We will follow this statement by a more detailed consideration of the problem, and a further statement of the conditions and the reasons leading to the conclusions stated.

SUMMARIZED CONCLUSIONS.

1st. Present Disposal: The diversion of the Chicago sewage from Lake Michigan, resulting from the Drainage Canal and other causes, has effected a remarkable improvement in the death rate from water borne diseases. The sewage nuisance in the streams of the Chicago district has been reduced^ to a large extent. This result has been accomplished, however, by transferring the bad conditions in Chicago to the Des Plaines and Illinois Rivers in which a crying nuisance has been created for more than one hundred

miles ; and by diverting large amounts of water from the Great Lakes, over strenuous objections from property owners claiming a right to the water diverted.

It is generally conceded that the present conditions should not be

allowed to continue. The Sanitary District is already engaged upon remedial measures through which a large part of the sewage will be treated before discharge into the Drainage Canal.

2nd. Population and Growth:

In planning works for sewage disposal, it is necessary to consider

the future population of the locality. It is not financially practicable

to make expenditures now for a problematical future. It is necessary, however, to determine the future populations approximately and to adopt works capable of construction in units that may be increased in capacity from time to time as occasion requires, without destroying previous expenditures. Thus each dollar expended will provide a link in a complete chain of sewage disposal works. We have examined the forecast of population as estimated by the

Sanitary District of Chicago, and we believe it represents future proba- bilities as accurately as required for the above purpose. This estimate

covering the population of the Sanitary District is as follows :

1920 census, 2,978,635 1930 3,710,000 1940 4,425,000 1950 5,140,000 1960 5,850,000 1970 6,580,000

In addition to the population in the Sanitary District, there is now (1925) a population of 180,000 in the northern Indiana cities bordering the lake and draining through the Calumet River. Under ordinary low flow conditions this drainage passes through the Sag Channel to the Main Drainage Channel and thus into the Illinois River. The Sanitary District includes about eighty-five per cent of the total population in the greater Chicago region which includes Cook, Kane, DuPage, Lake and Will Counties in Illinois, and Lake County in Indiana. The greater part of the outlying population has more or less effect upon the pollution of the lake and the nearby streams.

3rd. Amount and Character of Sewage:

The present discharge of the sewers within the Sanitary District

is about 800 miUion gallons per day. This is equivalent to a river 100 feet wide and five feet deep flowing one and one-half miles per hour. This sewage carries an organic load per capita greater than any other large city for which accurate figures have been available to us.

This excessive load is partly due to a few great industries which produce an 'amount of pollution estimated by the Sanitary District to be the equivalent of about 1,500,000 people (1920).

4th. Standard for Pollution:

In the consideration of sewage treatment works that wifl be re--

quired under various drafts of dilution water from Lake Michigan, it has been necessary to fix a standard of maximum pollution for the Chi- cago Drainage Canal in order that reasonable sanitary conditions may be maintained in the Des Plaines and Illinois Rivers. We suggest the following as a reasonable standard

The liquid discharged by the Drainage Canal, as evidenced by the average of representative samples taken for any thirty consecutive days shall, (a) Be practically free from settleable solids deposited in two hours, and, (b) Shall contain dissolved oxygen equal to or exceeding the biochemical oxygen demand of said liquid for five days when incubated at 20 degrees C. 4

(c) Shall contain not less than three parts per million of dissolved oxygen. The treatment works hereinafter outlined in connection with specified dilutions from the lake will meet this standard in our opinion.

5th. Protection of the Water Supply: Even under the heavy diversions from Lake Michigan in recent years and the generally favorable typhoid death rate, the quality of the water supply for Chicago has been far from satisfactory. This is due to the incidental pollution of the lake, periodic discharges from the Chicago and Calumet Rivers and other causes. Occasionally sporadic typhoid outbreaks have occurred attributable to the water. Safety is only secured by heavy dosages of liquid chlorine which are extremely objectionable to many people and which the Chicago authorities regard as closely approaching the maximum dosage tolerable. Compared to the usual standards applicable to clean water, the water is dirty most of the time, and it is quite turbid more than ten per cent of the time. Even when comparatively clear it often contains miscroscopic animal organisms no doubt harmless, but very objectionable to many people. The filtration of drinking water has been extensively practiced for more than twenty years. More than twenty million people are thus supplied in the United States. Many filtration plants handle a water polluted to a greater degree than Lake Michigan water would be under any diversions for dilution purposes considered in this report.

Chicago can secure pure clean water at all times by the filtration of its present supply. We regard this as the only means by which a satisfactory supply of water may be obtained, regardless of any practicable measures for sewage treatment or lake water diversions for dilution.

Filtration is considered as a pre-requisite to the adequate disposal of sewage in all projects considered in this report.

6th. Metering of the Water Supply:

At the present time ninety per cent of all water services in Chicago are served through so-called ''flat rates." The pumpage of water is excessive, pressures are deficient, fire protection service is jeopardized and the costs of water supply, intercepting sewers and sewage disposal are greatly increased over what would be necessary if water waste were restricted.

Universal metering of the water services is urgent. Metering alone will (a) Double the average pressure within the City of Chicago. 5

(b) Furnish all adequate water service where but twenty-five

percent now enjoy it. (c) Enable the present water works with but minor extensions to serve the City for the next generation. (d) Through the immense savings effected in deferred construction costs enable the City to install filtration works.

If universal metering of the Chicago Water Works is accomplished within the next ten years savings of from $200,000,000 to $225,000,000 will be effected prior to 1945. This amount is so great that in addition to financing the installation of meters and filtration works for the entire city, it would cover the cost of constructing the entire intercepting sewer and sewage disposal works required in the Chicago Sanitary District up to 1945 and leave a large surplus in addition. The costs of sewage disposal are also influenced by the waste of water. If universal metering of the water works services is not undertaken, the estimated costs of the interceptors and sewage treatment works outlined in this report must be increased by an amount of from $42,000,000 to $53,000,000 depending upon the flow available for dilution and the types of plants required thereby.

7th. Volume of Sezvage: The total quantity of sewage to be treated in the Chicago District may be taken as approximately equal to the total water supply. This assumes that infiltration into the sewers will be offset by that part of the water supply used for sprinkling and other purposes which do not contribute to the sewage flow.

At the present time, due to water waste, the pumpage of water in the Chicago District is excessive. The dry weather flow of sewage is correspondingly much larger than it would be if the waste of water were curtailed.

The total volume of sewage under metered and unmetered conditions has been estimated based upon the assumption that a ten year period beginning in 1925 and terminating in 1935 will be required to install meters on all water services in the City of Chicago, and that when all services are metered the sewage per capita, including industrial and all other uses, will be approximately 160 gallons per day. Under these assumptions the following table shows the estimated quantities for each five year period from 1925 to 1945. : 6

Million Gallons Sewage Daily. Present Conditicns Universal Year of Metering Metering 1925 877 1930 1,054 777 (50% metered) 1935 1,243 662 1940 1,437 711 1945 1,629 769 The installation of meters on all services will cause the sewage flow of 1945 under complete metering to be less than at the present time, when but ten percent of the services are metered.

8th. Intercepting Sezvers:

The Sanitary District has adopted tunnels for its intercepting sewers. This appears to be a logical conclusion in view of congestion on the ground surface. Intercepting sewers have been built or are under construction for all areas except the West Side and the Southwest Side. The intercepting sewers to serve these two areas will in general extend along both sides of the main channel and the north and south branches of the Chicago River beginning with Fullerton Avenue on the North Side and extending in a southwesterly direction to the site proposed for the West and Southwest Side plants along the Drainage Canal near Summit.

It is beheved that with universal metering these intercepting sewers should be designed of such capacity that they will carry a flow equivalent to 375 gallons per capita per day. This is approximately two and one-third times the average flow as it is estimated to be after the installation of meters.

It is believed that a 35-year period (i. e. to 1960) is that for which the design of interceptors should be economically and practically made for sewers constructed in tunnel, capable of duplication in the future without excessive costs. The 20 miles of intercepting sewers required for the West Side system have been estimated to cost $7,890,000. The 15 miles of sewers required for the Southwest Side plant have been estimated to cost $4,495,700.

9th. Sezvage Disposal Costs in Other Cities: Construction and operating costs of sewage pumping stations and treatment works in other cities were compared with similar costs incurred by the Sanitary District of Chicago in certain works already built. In making this comparison consideration has been given to the price basis when the work was done and the unit costs for labor and materials in the cities compared. We deduce the following conclusions from the comparison 7

(a) Recent intercepting sewer contract costs in Chicago have been substantially double those secured in other cities under like construction conditions. (b) The Calumet Imhoff tank plant, constructed by the Sanitary District of Chicago (after being credited with the reasonable cost of an experimental sprinkHng filter and activated sludge plant), cost approximately three tim.es the average of tank plants of similar type in other cities. (c) The Des Plaines activated sludge plant of the Sanitary Dis-

trict of Chicago cost approximately three times the average cost of similar plants in Milwaukee and Indianapolis. (d) The cost of operating the Calumet Imhoff tank plant (after being credited with the reasonable cost of operating a small sprinkHng

filter and a small activated sludge plant), is approximately four times that of operating similar plants in other cities when compared on the basis of cost per million gallons treated or ten times the average based on cost per capita served. (e) The cost of operating the Des Plaines activated sludge plant of the Sanitary District of Chicago is from eight to ten times that estimated to be necessary for the operation of the activated sludge plant at Milwaukee. (f) The cost of operating the 39th St., Lawrence Avenue and

Calumet pumping stations of the Sanitary . District of Chicago is approximately three times as great per unit of work performed as that of other stations of similar size and type in other cities.

10th. Basis of Cost EsPimates: All estimates of cost of construction and operation used herein are predicated upon labor and material prices prevailing in the Chicago District in the early part of 1925. The estimates are further based upon

the average efficiency which it is practicable to secure in public enter-

prises of similar nature ; no better and no worse than conditions recently prevailing in Detroit, Cleveland and Milwaukee.

11th. Types of Treatment Works: At the present time the Des Plaines activated sludge plant and the

Calumet Imhofif tank plant are in operation. The Sanitary District is also definitely committed to the construction of an activated sludge plant

at the North Side plant, the construction of which is about one-third completed.

All of the estimates herein made for all amounts of flow considered are based upon the Sanitary District's program of adding sprinkling

filters at the Calumet plant, and of building a sprinkling filter plant at 8 the Corn Products Plant and an activated sludge plant at the Stock- yards. The variations in degree of treatment required with the several flows considered, are all secured herein by applying different treatment processes to the West and Southwest Side plants.

All estimates of cost herein are in addition to contracts now let and under construction on the North Side intercepting sewerg and that part of the North Side disposal plant for which contracts have thus far been let. In our opinion the sites for proposed sewage disposal works are well chosen.

12th. Additional Works Required zvith 10,000 Cubic Feet Per Second Flozv:

A flow in the channel of 10,000 cubic feet per second will necessitate in addition to the sewage disposal works now constructed or under contract, preliminary or tank treatment of the sewage at the West Side plant and complete tank and sprinkling filter treatment for the South- west Side. The cost of additional purification works including intercepting sewers required with a total flow of 10,000 cubic feet per second is estimated at $57,415,240 to 1935 and $64,692,700 to 1945. The cost of operation of all pumping stations and sewage disposal plants with a flow of 10,000 cubic feet per second is estimated at $4,364,000 in 1935 and $5,004,800 in 1945.

13th. Required Works zvith 4,167 Cubic Feet Per Second Flozv: With a smaller amount of diluting water, complete secondary treatment of the sewages at both the West and Southwest Side plants would be necessary. Tanks and sprinkling filter treatment would not be suflicient by 1945. Activated sludge treatment is required to meet the 1945 conditions with but 4,167 c. f. s. flow available.

The estimated cost of all interceptors and disposal plants required with the flow of 4,167 cubic feet per second is $69,213,500 for 1935 conditions, and $76,583,300 for 1945 conditions. We estimate the cost of operating all sewage pumping stations and sewage disposal plants necessary with the flow of 4,167 cubic feet per second at $5,163,100 in 1935 and $5,817,600 in 1945.

14th. Required Works zvith 2,000 Cubic Feet Per Second Flozv:

With a flow as small as 2,000 cubic feet per second there is no practicable way of meeting the pollution standard herein suggested.

15th. Required Works zvith 7,500 Cubic Feet Per Second Flozv:

The 7,500 cubic feet per second flow requires that a complete sprinkling filter plant be built at the West Side and tanks at the South- 9 west Side. This will suffice up to as late as 1947 after which filters will be required at the Southwest plant also. The estimated cost of constructing all plants under this flow is $61,477,920 in 1935, and $67,- 926,100 in 1945. The annual cost of operating all pumping stations and disposal plants is estimated at $4,530,400 in 1935 and $5,137,000 in 1945.

16th. Required Works with 8,500 Cubic Feet Per Second Flow: The required works with 8,500 cubic feet per second flow would be the same as those required for 10,000 cubic feet per second flow. The construction and operating cost would be the same as those outlined under the project in paragraph above.

17th. Review of Expenditures Under Various Diversions: The expenditures for construction and operation of the treatment works required for 1935 and 1945 conditions with flows varying from

2,000 to 10,000 cubic feet per second are shown in Table 1. Increasing the flow from 4,167 to 10,000 cubic feet per second saves but sixteen and one-half percent in the expenditures required for sewage treatment, and but fourteen and one-half percent in the annual operating costs.

18th. Suggestion for Stockyards Wastes: The Sanitary District program contemplates a separate sprinkling filter plant at Argo and a separate activated sludge plant for the Stock- yards wastes. Other cities in which the packinghouse waste per capita contributing sewage is as great as that at Chicago have found it practicable to treat this waste, mixed with the domestic sewage, at either sprinkling filter or activated sludge plants. At Chicago the Southwest Side intercepter passes almost directly by the Stockyards, which sug- gests the further practicability of combining this concentrated waste, after the removal of the coarse solids, with the domestic sewage before treatment. If treatment of the Stockyards waste, mixed with the sewage of the West and Southwest Side, is practicable on stone filters, there will result a saving in construction cost of from $2,300,000 to $3,500,000. There will also result a saving in annual cost of operation of $350,000 per year, even after crediting an income of $360,000 per year from the sale of the sludge from the activated sludge plant. This annual saving capitalized at four percent adds a further sum of $8,500,000, making the ^ total capitalized saving between $10,800,000 and $12,000,000.

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PART II.

PRESENT DISPOSAL OF SEWAGE AND DEFICIENCIES

Chicago, and the industrial region surrounding it, occupies the

Southwestern shore of Lake Michigan. The ground is comparatively low. The greater part of it Hes less than 20 feet above Lake Michigan. This entire region formerly drained naturally into the lake through the Chicago and Calumet Rivers. That locality now constituting the western suburban area, however, is tributary to the Des Plaines River, which parallels the lake shore about ten miles inland, the waters of which are tributary to the Mississippi river system through the Illinois river.

More than three milHon people now occupy this territory. It is conservatively estimated that the population will double within the next thirty years. The present flow of sewage is about 800 million gallons per day. This is equivalent to a river 100 feet wide and five feet deep flowing one and one-half miles per hour. The shore line of Lake Michigan from Gary on the south to Wau- kegan upon the north is about seventy-five (75) miles in length. More than half of it is densely populated. Much of it is occupied by industries.

The northern one-third of it is residential in character.

Development of Sewers. Sewers were built as required, draining immediately to the nearest water outlet. The earliest settlement of considerable size, was located at the mouth of the Chicago river. In this locality all sewers drain directly into the river or into its north or south branch. As the population extended northward and southward, sewers were built discharging directly into the Lake. When sewers became necessary in the region adjoining the Calumet River, sewers were built discharging directly into this stream. The construction of sewers in Chicago was begun in 1856. At this time the population was about 80,000. Thereafter the growth of the city was very rapid. The mileage of sewers kept pace with the population for in many localities the habitation was not practicable until sewers had been built.

Early Disposal of Sewage. Sewers discharging into the Chicago River and branches ultimately reached the lake except for a small amount, which from the earliest use 13

of sewers, reached the old IlHnois and Michigan canal by pumping, and thus passed to the Des Plaines and Illinois Rivers.

Illinois and Michigan Canal.

The Illinois and Michigan canal was completed in 1848. It parallels the Drainage Canal a few hundred feet to the south. Its water supply was obtained partly by gravity from the Calumet River and partly by water pumped from the south branch of the Chicago River. From time to time the pumping works were increased in capacity, which temporarily tended to improve the foul conditions in the Chicago River, and to divert some of the sewage from the lake.

Water Supply.

The water supply for the City of Chicago and for all its suburbs bordering the lake is taken from Lake Michigan. Public Water Works for Chicago began operation in 1856. Water was taken from the lake at the foot of Chicago Avenue, about one mile north of the mouth of the

Chicago River. As the occupied area of the city grew it became necessary to construct additional Water Works' intakes, and as the pollution from the sewers was constantly increasing, the intake cribs were progressively located farther from the shore.

At the present time the city is supplied through six cribs varying from two to four miles distant from the shore line. In the years of rapid municipal growth up to 1890, the sanitary conditions in the outlet streams, particularly the Chicago River and its branches, became progressively worse. Comparatively great accumula- tions of filth were washed into the lake, and occasionally reached the Water Works' intakes. This resulted in the general prevalence of typhoid fever, and occasional epidemics.

Drainage Canal.

We will not recite here all the steps that were taken to bring about an improvement in the sanitary conditions. These matters, while of general interest, are recited elsewhere, and bear only indirectly upon this problem. The most important step taken toward improving conditions was the passage of the State law creating the Sanitary District of

Chicago and empowering it to construct the Chicago Sanitary Ship Canal, May 29th, 1889.

The Drainage Canal is twenty-eight miles long from the Chicago River at Robey Street to the Controlling Works at Lockport. It creates a reversal of the flow of the Chicago River, and in addition it draws in certain quantities of water from Lake Michigan, depending upon its controlled rate of flow. The flow is controlled at the foot of the Canal. 14

This work was started in 1892 and completed January 2, 1900. The flow capacity of the main channel is approximately 10,000 cubic feet per second. In 1907 the canal was extended beyond Lockport, a distance of about four miles to concentrate an available fall of about thirty-four feet, and utilize the same in the development of a water power in dropping the canal flow down to the level of the Des Plaines River. Since the completion of this power plant it has generally formed the means for regulating the flow of the Drainage Canal, although the flow can also be regulated at the Controlling Works, four miles upstream.

In connection with the utilization of the main drainage canal it was necessary to improve the Chicago River in order to permit the desired flow without interfering with navigation. The river was widened and deepened at various places between the years 1897 and 1920. In 1910 the north shore channel was completed connecting the north branch of the Chicago River with Lake Michigan at Wilmette. At this place a pumping station was built operating at about three feet head. This canal and pumping station serves the purpose of pumping fresh water into the head of the north branch of the Chicago River, thus improving the sanitary conditions therein, resulting from the large amount of sewage received. This channel is eight miles in length and has a capacity of 1,000 cubic feet per second.

The Calumet Sag channel taps the little Calumet River at Blue Island diverting the water thereof westerly and joining the main drainage canal at Sag. This canal was completed in 1922. It has a length of sixteen miles and a capacity of 2,000 second feet.

Intercepting Sewers.

With the opening of the Drainage Canal January 2, 1900, all sewage discharging into the Chicago River and branches was diverted to the Illinois River. There remained, however, a considerable amount of sewage which reached the lake, through the sewers discharging directly therein. To stop this pollution a system of intercepting sewers along the lake shore was planned and built by the City of Chicago. All sewage entering the lake, between the Chicago River on the north and 87th St. on the south, is now intercepted by a main sewer on Stony Island Avenue running north from 83rd St. and thence following Cornell Avenue and the shore of Lake Michigan to 39th St. At this place the 39th St. pumping station lifts the sewage to the twenty feet sewer running west on 39th St., entering the south branch of the Chi- cago River. This station is also equipped with pumps to take dilution water directly from the lake for the purpose of keeping the south fork of the river clean. Plans are now under yvay to extend the 39th St.

Figure 1.—Map of the Sanitary District at Chicago and irtelnltar. 15

sewer so that it will enter the drainage canal at Western Avenue near 31st St. This will obviate the necessity for dilution water in the south branch of the river. The southern part of the Stony Island Avenue district is pumped into the Stony Island Avenue sewer by pumping station constructed and operated by the City of Chicago at 73rd St. and Stony Island Avenue. The South Side intercepting sewer was completed in 1907. The North Side sewers entering the lake were intercepted by the construction of sewers paralleling the lake shore running north to Law- rence Avenue, and from Howard Avenue running south to Lawrence Avenue. At Lawrence and Racine Avenue a pumping station was constructed, discharging the sewage westward into the north branch of the

Chicago River. This station is also equipped with pumps to draw dilution water from Lake Michigan for the purpose of improving the character of the water in the north branch of the Chicago River. A similar system of intercepting sewers north of Howard Avenue lead to the Evanston pumping station at Orrington Avenue and Lake Street, which intercepts the remainder of the lakeward flowing sewers south of Wilmette and discharges the sewage into the north shore channel. All sewage originating in the Sanitary District north of Wilmette is intercepted by a system of sewers terminating at the north shore channel and Sheridan Road. The Wilmette pumping station, located at this point, is equipped with pumps to draw dilution water from the lake for the purpose of maintaining cleanly conditions in the north shore channel and the north branch of the Chicago River. The North Side intercepters, within the City of Chicago, became effective in 1908. The intercepting sewer system north of Wilmette became fully effective in 1916. The Evanston sewer and pumping station was completed in 1921.

Calumet Region.

Sewage within the City of Chicago, south of 87th Street, has here- tofore been discharged directly into the Calumet River, and considerable of it still reaches the river. This will very shortly be corrected by the completion of the Calumet intercepting sewer and the pumping station at 95th Street and the Calumet pumping station at Indiana Avenue and

125th St. With the completion of these sewers all sewage south of 87th St. will be pumped into the Calumet Sag Channel after treatment, and delivered to the Chicago Drainage Canal at Sag.

The Sag Canal does not reverse the Calumet River system at all times, the flood flow of this stream greatly exceeding the capacity of 16 the Sag Canal. Periodic discharges from the Calumet River have been a serious menace to the water supplies, particularly those near the mouth of the Calumet. This menace will continue to a greater or less extent.

TABLE 2. FLOW IN MAIN CHANNEL. Authorized Flow Actual Flow by State Law V_/U.. H L. jJtJl Oct/. Year X^OpUldllOIl r I. per oec. as Corrected. 1900 1,640,000 5,467 2,990 1901 1,688,000 5,627 4,046

1902 1,736,000 5,787 4,302 1903 1,934',000 6,447 4,971

1904 1,985,000 6,617 4,793 1905 2,035,000 6,783 4,480

1906 2,090,000 6,967 4,473 1907 2,144',000 7,147 5,116

1908 2,195,000 7,317 6,443 1909 2^250^000 7^500 6,495

1910 2,308,000 7,693 6,833 1911 2,370,000 7,900 6,896

1912 2,432,000 8,107 6,938 1913 2,509,000 8,363 7,839

1914 2,589,000 8,630 7,815 1 790 lyio 2,652,000 8,840 I, too

1916 2,716,000 9,053 8,200 1917 2,782,000 9,273 8,726

1918 2,846,000 9,487 8,826 1919 2,916,000 9,720 8,595

1920 2,986,000 9,953 8,346 1921 3,063,000 10,210 8,355

1922 3,143,000 10,477 8,858 1923 3,214,000 10,713 8,348

1924 3,284,000 10,947 9,465

*These quantities have been computed from the latest available data. Note—From Report of Engineering Board of Review,

Diluting Water.

It was the original idea in the construction of the Drainage Canal that the sewage of the Sanitary District would be diluted by mixing with a sufficient amount of fresh water from Lake Michigan to render the mixture innocuous, and to assist in the natural purification of the sewage in its transit through the Drainage Canal and the river system Id Ql

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Figure 2.—Hydrograph for Chicago Drainage Canal and Illinois River at Peoria, 1I00>19S4. Flow of Illinois River as reported bv U. S. O. S. except year 1900, which is estimate by J. A. Harman. 17 below same. Table 2 shows the average flow at the outlet of the Drainage Canal for each year since the canal was opened in 1900. This flow was limited in the early years by the ability to get the water through the Chicago River. Within the past ten years the flows have been more nearly up to the pollution requirements of the population served, but they have never been adequate to properly care for the sewage and trade wastes. The table also shows the estimated amounts of flow required by the State law creating the Sanitary District, under which a minimum dilution of three and one-third second feet per thousand people was required. The above flows include the sewage, as well as the diversion, for

dilution purposes. Water for both purposes is taken from the lake.

The present Hquid volume of the Chicago sewage is approximately 1200 second feet or about twelve percent of a total diversion of 10,000 second

feet.

Additional Dilution.

Immediately after passing the controlling works at Lockport the Drainage Canal water joins the natural flow of the Des Plaines River.

The flow of this stream during the late summer and fall is usually negligible. Large flows of fresh water are, however, brought in during the flood seasons.

Below Joliet the principal tributary is the Kankakee River, which joins the Des Plaines forming the Illinois River. The next principal

tributary is the Fox.

The net effect of all these streams and other minor tributaries com-

ing in above Peoria is indicated on Figure 2, which shows graphically the flow of the Illinois River at Peoria, and the flow of the Chicago Drailiage Canal since the latter was opened in 1900, During the past ten years the flow of the Drainage Canal at Lockport has generally ranged between 8,000 and 9,000 second feet. During the two dryest months in the year the additional flow coming in above Peoria has usually ranged between ten and twenty per cent of the Drainage Canal flow. During the remainder of the typical year this additional inflow has been considerably more, possibly averaging as much as a fifty percent addition of fresh Avater. During several months of nearly every year the additional water coming in has been fully equal to the flow of the Drainage Canal.

In certain months of heavy flow it has been four to five times as great as the Drainage Canal flow. During the year 1924, which was a year of sustained natural flow in the Illinois river, the tributaries above Peoria brought in a flow of fresh water fully equal to the Drainage Canal flow throughout the year up to and including September. :

Sewage Treatment Works. Realizing the inadequacy of dilution as a permanent solution for the Chicago sewage problem, the Sanitary District some years ago began experimentation and the preparation of plans for sewage disposal works to supplement the dilution project. Up to the present time treatment works have been built as follows

Des Plaines River Treatment Plant.

The Des Plaines plant is located at Roosevelt Road and S. 1st Avenue, Maywood. At this place a system of intercepting sewers terminates, draining an area of 18.5 square miles between North Avenue and 22d St., and west of Harlem Avenue. The present population served is approximately 39,000. This plant serves the towns of Maywood, Melrose Park, Forest Park, River Forest, the north part of Oak Park, and the U. S. Government Speedway Hospital. This plant began operation in August, 1922. It consists of a pumping plant, an electric driven power plant and treatment works by the activated sludge process, including a dewatering plant for sludge.

The capacity of the plant is four million gallons per day slightly less ; than this amount of sewage is being treated at present. This plant has been designed with the view to experimentation in order more effectively to plan the larger plants subsequently to be built.

Calumet Treatment Works.

The Calumet Treatment Works is located near E. 125th St. adjoining the west shore of Lake Calumet. It is intended to serve all the territory south of 87th St. Sewage will be delivered by the Calumet pumping station. Purified effluent will be discharged into the Calumet

Sag Channel. The area to be served is approximately 42.5 square miles. It has a present population of 179,000 of which approximately 100,000 reaches the plant at present. The plant consists of a system of Imhoff tanks having an estimated daily capacity of 55 M. G. D. The plant was put in operation in Sep- tember, 1922. A small activated sludge plant and a small trickling filter are also in operation at this site for experimental purposes.

Other Works.

The Sanitary District includes forty-nine incorporated cities and villages, many of which are so located as to make it economical to solve their problems separately. 19

Figure 3.—Map of the Sanitary District of Chicago showing sewage treatment projects and intercepting sewers. (Scale appox. 1 inch = 6 miles.) 20

The District has built, and is operating a small settling tank and trickling filter plant at Morton Grove, completed in 1914, serving J200 people. A small plant has also been completed at Glenn View. Minor treatment projects are proposed for the towns of LaGrange, Brookfield, LaGrange Park, North Brook, Oak Forest, Posen Robins, Upper Des Plaines Towns, Harvey and Schiller Park. Other miscellaneous plants will ultimately be required for outlying towns.

North Side Plant.

Work is now well under way covering the North side sewage treatment project located at Howard Avenue, immediately west of the North Shore Channel. This plant will consist of a pumping station, an electric driven power plant and an activated sludge plant. As now being built

it will have a capacity of 175 M. G. D., and it will be subject to indefinite enlargement by the addition of units. Sludge will be pumped to lagooning beds southwest of the city. The disposal tract covers 188 acres. The project serves all territory in the Sanitary District lying north of Fullerton Avenue. Area sixty-

two square miles. Present population (1927) is approximately 737,000.

The plant is scheduled for completion in 1928.

West Side Sewage Treatment Project.

This treatment project is proposed to serve an area of 57.5 square miles, embracing the heart of Chicago, and lying between Fullerton Avenue on the north and 31st St. on the south, and extending from Lake Michigan westward, including the loop district of the city. The

population at the present time is about 1,340,000. The plant will be located adjoining the north bank of the drainage canal somewhere in the vicinity of South Harlem Avenue. Plans for this plant have not been

made. It is tentatively proposed to use sedimentation tanks, supplemented by sprinkling filters when necessary.

Southzvest Side Treatment Works.

A similar plan is proposed for the Southwest side embracing all remaining territory in the City of Chicago north of 87th St. and south

of 31st St., lying south of the drainage canal. This comprises an area of 59 square miles. The population at present is about 910,000. Some parts of the district are sparsely settled.

Industrial Wastes Treatment Projects. A very important part of the organic load contained in the Chicago

sewage is contributed by certain industries, particularly the packing industries located near the head of the Drainage Canal. Also the Corn 21

Products Company located at Argo on the Drainage Canal and near the western city limits. The Packing Town wastes and the Corn Products wastes are de- rived from comparatively small areas respectively. The wastes are highly concentrated and require special treatment. Thoi:ough studies have been made in cooperation with the industries. Plans have been made to treat Packing Town wastes by the activated sludge process. Further experimentation at the Corn Products plant is now under- way. The experiments to date indicate that the wastes can best be treated by sprinkling filters.

Effectiveness of Disposal Operations. The diversion of the sewage from Lake Michigan has been followed by a remarkable reduction in typhoid fever in the City of Chicago. A number of other matters have contributed to this improvement, including the chlorination of the water supply which was begun in 1912, the pasteurization of milk begun in 1910, and also no doubt other important causes outside of the Chicago district, which have been instru- mental in very greatly reducing the typhoid death rates throughout the United States. Table 3 shows these facts in tabular form.

Condition of the Lake.

Lake Michigan is still badly polluted in the Indiana Calumet region, from the Indiana cities and the periodic discharge of sewage from the southern part of Chicago, a part of which still reaches the Lake. There have also been periodic, but relatively infrequent sewage discharges from the Chicago river due to flow reversals caused by floods. Minor pollution still reaches the lake from the suburban towns north of the

Sanitary District. This pollution is comparatively small, and will probably become less with improved conditions in the North Shore Sanitary District, embracing certain suburban towns north of the Cook County line. Particularly at times of great storms the sanitary condition of the water at the Chicago intakes is very bad. This subject will be discussed hereinafter.

River Conditions. During recent years the main channel of the Chicago River through the heart of the city, while not seriously objectionable, nearly always contains evidence of floating sewage. Conditions in the north branch of the Chicago River generally range from bad to fair, depending upon the extent of operation of the dilution pumps. The south branch of the river to the head of the Drainage Canal increases in foulness as the 22 additional sewers join the stream. The Drainage Canal throughout its length, as would be expected, always bears evidence of the heavy sewage load carried. Odors on the banks are usually noticeable, but conditions only become very foul during the summer and early fall months.

At Lockport dissolved oxygen is normally exhausted during the warm weather season. A similar condition prevails generally throughout the Illinois River to the head of Peoria lake about ninety-six miles

TABLE 3.

ANNUAL TYPHOID FEVER MORTALITIES IN CHICAGO PER 100,000 POPULATION.

From Report of Engineering Board of Review, and Supplemented.

Typhoid Percent Fever of Total Years Mortality Mortality Remarks 1867 73.3 3.45 1868 79.3 3.34 1869 65.3 2.82 1870 87.4 3.66 1871 61.0 2.92 1872 142.6 5.16 1873 71.6 2.85 1874 53.4 2.63 1875 51.7 2.62 1876 41.2 1.96 1877 37.0 1.98 1878 33.4 1.97 1879 42.3 2.41 1880 34.0 1.63 1881 105.2 4.03 1882 82.4 3.49 1883 62.2 3.12 1884 56.2 2.84 1885 74.6 3.98 1886 68.6 3.53 1887 50.3 2.48 1888 46.7 2.38 1889 48.4 2.67 1890 91.6 4.61 1891 173.8 7.20 1892 124.1 5.68 1893 53.5 2.47 1894 37.5 2.06 1895 37.9 2.14 1896 52.6 3.23 1897 29.3 2.00 23

TABLE NO. 3—Continued.

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J? C V cx KJL X. yj Lctl Years Mortality Mortality Remarks 1898 40.8 2.79 1899 27.2 1.73 1900 19.8 1.35 Opening of Drainage Canal 1901 29.1 2.09 1902 44.5 3.03 1903 31.8 2.03 1904 19.6 1.42 1905 16.9 1.21 1906 18.5 1.27 Opening South Side Interceptors 1907 18.2 1.16 Completion South Side Interceptors 1908 15.8 1.09 Opening North Side Interceptors 1909 12.6 0.87 1910 13.7 0.90 Pasteurization of Milk 1911 10.7 0.74 Completion North Shore Interceptors 1912 7.6 0.51 Chlorination of Water Started 1913 10.6 0.71 1914 6.9 0.49 1915 5.3 0.37 1916 5.1 0.35 1917 1.6 0.11 Complete Chlorination of Water 1918 1.4 0.08 1919 1.2 0.09 Completion Evanston Interceptors 1920 1.1 0.09 1921 1.1 0.09 Completion Calumet Interceptors 1922 1.1 0.10 1923 1.9 0.16 1924 1.5 0.13 24

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Analytical Studies.

The most accurate picture of the sanitary conditions in the Des Plaines and Illinois Rivers, below the outlet of the Chicago Drainage

Canal, is furnished by the comprehensive study of the U. S. Public

Health Service, covering fourteen months beginning July 1, 1921, and ending August 31, 1922. A complete report of this investigation has not yet been printed. There has been furnished to us, however, a series of tabulations, summarizing the principal results. ;

It was the purpose of this investigation to determine the extent of pollution, the character of the water at various places within the streams and the factors that particularly affect the decomposition of the organic matters discharged therein. Twenty-seven sampling stations were established between Lockport and the mouth of the Illinois River. Samples were collected daily, or, at certain points tri-weekly, from mid-depth of the stream. At the stations between Lockport and Shanahan, the latter place just above the mouth of the Kankakee, samples were collected from the center of the stream. At all stations below Shanahan samples were taken at three points from the cross section. Samples were carefully taken, iced and promptly transported to the nearest laboratory.

Examination of samples was made in all cases in less than three hours. The average time was much shorter. The report of the preliminary examination states : "Due to fluctuations in the sewage strength from night to day at the outlet of the Sanitary canal, and to the variation in flow caused by opening and closing of the gates at the power plant above

Joliet, it is probable that the results of analyses recorded in the tables which follow do not represent exactly the average condition throughout the day of the water at the sampling point." The tabular data, accompanying the preliminary report, is too bulky to present in full. We summarize the principal features of it on Figures 5 to 8 inclusive. We show upon these diagrams the average dissolved oxygen for each month during the investigation at each of the sampling points. Also the five day bio-chemical oxygen demand for the same places and times. These determinations represent the character of the water from the pollution and nuisance standpoints. The bio-chemical oxygen demand is representative of the amount of organic pollution carried. The dissolved oxygen represents the possibility of local nuisance and the practicability of existence of the natural water life of the stream. Both determinations considered progressively down-stream indicate the degree of improvement in the sanitary character of the water flowing.

Winter Conditions. We show separate diagrams intended to indicate typical conditions in the four seasons of the year. In the winter time the dissolved oxygen - is high in the water taken from the lake on account of its low temperature. It will be observed that at no point between Lockport and the mouth of the Illinois does the dissolved oxygen fall below 7.5 p. p. m. further there is very little reduction in the dissolved oxygen throughout the travel of the water from. Lockport to the Mississippi. The net total effect is an increase. 27

The organic matter (as represented by 5 day b. o. d.) is very high at Lockport, averaging generally from twenty to twenty-four p, p. m.

Near LaSalle it has been reduced about two-thirds in p. p. m. and about one-third in the total load carried by the stream, allowing for the additional dilution water coming in from the tributary streams above

LaSalle. The improvement is probably due largely to sedimentation supplemented by a small amount of oxidation. Between LaSalle and 28

Peoria the improvement is much greater by reason of further sedimentation in the wider and deeper river between LaSalle and Peoria. The diagrams plainly show the additional pollution reaching the Illinois River at Peoria and Pekin, and the improvement of the stream below Havana. In the v/inter season there is apparently practically no improvement in the quality of the sewage and dilution water between Chi- cago and Lockport. At this season of the year each sewer drops its

cr oo f- vx) 29 load into a stream of ice cold lake water. Practically speaking, the sewage travels in cold storage to Lockport and throughout its course to the Mississippi River. Apparently the principal improvement in the character of the stream is due to sedimentation.

Summer Conditions. The summer conditions present a very different picture. At this season of the year organic decomposition reaches its maximum, producing a heavy demand on the oxygen in the stream with a tendency to produce putrefactive conditions with attendant odors and a reduction in the oxygen to the point where the natural water life of the stream may be suffocating. At this season the mixture of sewage and lake water, as delivered at Lockport, has an organic load slightly more than half that contained in the winter season (5 day b. o. d.). This probably results from oxidation and septic action in the Drainage Canal above Lockport, the 30 result of the decomposition being carried away partly in gases and partly in inert matter carried along with the water in suspension. At this season oxygen is practically exhausted in the Drainage Canal between Chicago city limits and Lockport. It does not exceed 1 p. p. m. at any place above Chillicothe, 110 miles below Lockport. Between

Chillicothe and Peoria the stream rapidly recovers its oxygen in its traverse through Peoria Lake. This is due to the reduction in organic :

31 matter that has taken place up-stream, oxygen absorption from the atmosphere on the large surface of Peoria lake, and the product of oxygen-producing aquatic vegetation. Below Peoria and Pekin there is a further draft upon the oxygen resulting from added pollution. It is considerably reduced at the mouth of the Illinois. From Peoria to the mouth, however, the Illinois River contains sufficient oxygen to permit a thriving natural water life. The reduction in the organic matter (5 day b. o. d.) is somewhat greater than in the winter time, taking into consideration the comparatively small amount of diluting water coming in from the natural streams below Joliet. The organic load has been reduced nearly two-thirds from Lockport to Peoria. It suffers a large increase at Peoria and Pekin and is again reduced in traveling to the mouth of the stream. As would be expected, from the absence of oxygen, between Lock- port and Chillicothe the river is in a very foul condition. It is entirely devoid of natural stream life. It is possible for sewage organisms only to live in this water. Below Chillicothe the rapid increase in the dissolved oxygen creates a very different condition. Below Peoria in

1921-22 conditions probably permitted the presence of fishes of all kinds naturally inhabiting the stream.

Spring and Fall Conditions.

The spring and fall conditions typify the transition from the winter conditions to the summer conditions, and from the conditions of summer to the conditions of winter. This is due to the gradually warming water in spring as summer is approached, and the gradual chilling of the water between September and November. This effect is plainly evident on Figures 6 and 8. Each diagram carries a tabular statement of flow from Joliet to Peoria. Attention is invited to the month of April, 1922, in which the flow at Peoria was nearly five times the flow at Joliet.

The effect of this additional dilution water is evident in the reduced organic content (5 day b. o. d.) at Peoria. Allowing for this dilution the total organic load of the stream at Peoria is apparently reduced to fifty percent as compared to the vicinity of Lockport, indicating that the agencies of oxidation and possibly sedimentation persist in floods.

Past Conditions—Illinois and Des Plaines Rivers.

What has been said above typifies as accurately as possible conditions which prevail at present. These conditions have been progressively growing worse since the Drainage Canal began to operate in 1900. The following is quoted from a recent statement of Dr. Stephen A. Forbes, Chief, State Natural History Survey Division, Illinois Depart- ment of Registration and Education 32

"A serious and practically continuous study of the system of the plant and animal life of the Illinois River was begun by the State Natural History Survey of Illinois in 1894 and has been continued with only one important interruption to the present year. The actual periods of active field operations on the river were as follows: 1894-1899 inclusive, 1901-1903, 1909-1912, 1913-1915, 1918, 1920, and 1922-1924. The interval of five years after 1903 was given mainly to the preparation and publication of a final report on the fishes of the State.

"We have had from the very beginning until now the continuous cooperation of the Water Survey of the State, upon which we have depended for chemical tests and analyses, and for bacterial data.

"Our reason for so prolonged attention to a single subject is found in the progressive changes in the stream itself, its content, and its environment, which have worked corresponding changes in the aspect and internal order of its biology, requiring frequent repetition of our studies and a consequent revision of our conclusions. The most important of these changes have been the introduction of the European carp in 1885 and its enormous multiplication until it has become more abundant than all the other fishes of the stream taken together; a general diking and reclamation of the very extensive bottomlands of the river and the draining of their numerous lakes; and a rapidly increasing pollution of the stream by sewage wastes from towns on its banks, and especially from the Sanitary District of Chicago. It is a very difficult matter to disentangle these several causes of change in a way to distinguish clearly their separate biological aspects. There was, for example, a large and rapid increase in the fisheries yield of the river at about the time of the opening of the sanitary canal in 1900, sometimes attributed to the canal itself, but largely due to a rapid multiplication of the carp before 1900; and there has been of recent years a general falling off in the fisheries yield coincident with increasing pollution of the stream, but this is in great measure consequent upon a restriction of the overflow of levees and the draining of the lakes. "In this confusion of causes and effects, it is quite impossible to show clearly and fully just how and to what extent the remarkable fisheries yield of the river, amounting in 1908 in prices paid to fishermen, to a dollar for every two feet of its length, has been affected by sewage pollution, but I must do what I can to this end in the brief time alloted.

"The injurious biological effects of pollution of the Illinois River by raw sewage from Chicago have, of course, varied widely according to a number of local and temporary conditions. Being greatest at the upper end of the river at mid-summer temperatures, and at low water, and increasing with the population of the Sanitary District and with the activity of operations at the Chicago Stock Yards, they have diminished downstream, with lower temperatures of the advancing season, and with the rise of the river levels. At their worst they have destroyed or driven from the upper Illinois all its clean-water plants and animals, including, of course, its fishes, substituting for them those normal to septic or pollutional conditions. In the mid- summer of 1911 the upper ten miles of the river were practically a septic tank, the gases of the bottom sludges being 79% methane; 19% carbon dioxide; 1.02% nitrogen; 0.56% carbon monoxide; 0.03% oxygen. There 33

were no fishes in that part of the stream, or for many miles below, and no moUusks or crawfishes on the bottom, the only animals there being sludge worms, certain midge larvae, and other foul water forms able to live without oxygen on the crude sewage precipitates. From this extreme condition there was a gradual shading off downstream until at a distance of sixty to seventy miles from the point of entrance of Chicago sewage the plant and animal life of the stream was virtually normal. Seven years later, however, that is, in 1918, pollutional conditions had moved downward some 60 miles farther, the river being at this time nearly deserted by fishes as far as the Peoria lakes, 93 miles down the stream, characteristic sewage organisms having extended their range in thrifty condition to 77 miles from its origin, and the areas of offensive pollution, distinguished by a stinking sludge containing an abundance of sewage worms and no clean water organisms, had moved downstream from Ottawa to Lacon, a distance of 51 miles,

"An expansion of the river 17 miles long and up to a mile in width, known as Peoria Lake, (although really a chain of three lakes connected by so-called narrows) served as a partial barrier to a further extension of the conditions of the upper river until the period of the world war when, coincident with an enormous increase in the organic wastes of the Chicago stockyards, these pollutional conditions were still further extended and intensified, culminating in 1920 in a virtual extermination of the original life of the river bottom as far down as Peoria Lake and in the lake itself and in the substitution for it of plants and animals usually to be found only in heavily polluted water.

"With the close of the war and a diminished outpouring of stockyards sewage, there has been a noticeable improvement of conditions in Peoria Lake, although in 1922 they were still far below their pre-war status; but in this year 1924, which has been characterized by an extraordinary high water level of unexampled long continuance, Chicago sewage has been so far diluted that fishes have ascended the stream to LaSalle, 60 miles above Peoria and only 50 miles from the river head,

"There seemed at one time to be good general ground for believing that the addition of household sewage to a stream might increase its fisheries yield, especially where, as in the Illinois River, this addition was made far enough above the more productive fishing grounds to permit the oxidation of nitrogenous materials and their conversion into forms available as food for fishes young or old, but our more recent computations show that there has always been an abundance of food in the Illinois River for a much larger stock of fishes than it carried—that the food supply, in other words, has not been the limiting factor in the river fishes, and that an increase of it consequently could not be a benefit,

"The product of this present season's operations on the river has not yet been sufficiently worked up to give us more than fragments of the biological picture, but one feature may be of special interest to sanitary engineers. We found in the summer of 1911 that heavy rains at a given point, followed by a rise in the river, increased the organic contents of the water and diminished the ratios of dissolved oxygen, the latter effect being continued downstream as putrefaction increased, so that oxygen ratios were actually diminished downwards instead of increasing as they usually do; and this 34 effect of local contamination by washing rains was still more clearly shown this summer by bacterial data contributed by the State Water Survey. Taking, for example, two points below Peoria which were six miles apart with a tributary stream between them; on July 31 the water at the upper- most of these points averaged 8000 bacteria to the c. c. and that at the lower point 32,000, while on August 8, soon after a very heavy rain, when the upper count was 4,000 instead of the former 8,000, the lower count was 120,000 instead of the former 32,000, this jump in numbers being evidently due to the muds swept in from the tributary after the storm.

"Time fails me to attempt to follow the effect of Chicago pollution beyond the wide water of Peoria Lake, where the situation becomes com- plicated, indeed, by a heavy addition of fresh sewage from Peoria itself and from the city of Pekin, 9 miles below, and it is certain that in 1920 this lake barrier was being forced and that the life of even the lowest of the chain of three was far from normal—that the lakes were delivering to the river beyond a considerable part of the load of trouble which they had received from above."

It is impracticable definitely to show the progressive deterioration in the quality of the water in the Illinois River throughout the entire period during which the Drainage Canal has been contributing flow, for the reason that during this period of twenty-five years the technique of water analysis has changed so that results cannot be compared numer- ically. No such comprehensive studies as that undertaken by the U. S. Public Health Service have been made. More or less fragmentary studies, however, indicate the increasing pollution with the growth of the population and industries in Chicago. We show on Figure 9 a series of dissolved oxygen readings made by the State Water Survey covering six round trips between July 22nd and September 11th, 1911, a single trip between July 11th and July 13th, 1912, a single trip between August 28th and September 3rd, 1918, and four round trips between July 15th and September 17th, 1920. This diagram indicates that in 1911 the summer oxygen content was fairly satisfactory up-stream as far as Marseilles. In 1918 and 1920 the conditions were very similar to those typified by the Public Health studies as far south as Chillicothe.

Ice Conditions.

Although the conditions on the Illinois River during the winter are generally favorable as regards nuisance, and not particularly detrimental to the natural life of the stream, yet occasionally protracted cold weather and an unusually extensive covering of ice brings about unfavorable conditions During the winter of 1924 and 1925 this unfavorable condition prevailed. An investigation under the direction of Dr. Forbes brought out the following facts. In Clear Lake, below Pekin, the dissolved oxygen con- . ;

35 tent of the water varied from 0.4 to 1.8 p. p. m. All kinds of fish were found to be dead in set nets and also under the ice outside of the nets. At Quiver Lake, just above Havana, where the water contained 2.5 buffalo gars p. p. m. a river seine hauled under the ice gave carp, and

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all stupid, pallid in color and of a disagreeable odor called "gassy" by fishermen, characteristic of fish taken from polluted water. At Tread-

way Lake, near Meredosia, where the oxygen content was 5.4 to 5.8^ practically the entire variety of river fish were being taken in hoop nets, all in good condition. Similar conditions were noted by the State Natural History Survey

in 1912. This condition unfavorable to fishes is brought about through organic pollution in the water, coupled with the inability of the stream

to replenish its oxygen supply from the air. That these conditions are

due to sewage pollution is shown by recent observations of Dr. Forbes* department, referring to Clear Lake, Quiver Lake, Coleman and Tread-

way Lakes. Also in Quiver Creek. Clear Lake is the farthest upstream

and contains only river water which begins to enter into it when the

river is three and one-half or four feet above low water mark at Peoria. Conditions there were as previously described. Quiver Lake receives water continually from the river, but also from Quiver Creek, an un-

polluted stream. Its condition is consequently not so deadly as that of

Clear Lake, although the mass of its water comes from the river. Treadway and Coleman Lakes are 8 or 9 miles above Beardstown,

on the same side of the river and a little distance below the mouth of the Sangamon, an unpolluted stream, from which they receive a large part of their water.

Investigations in the above lakes show a gradation from practical complete destruction of fish under the ice at Clear Lake, most open to pollution, to normal conditions at Coleman and Treadway Lakes, also frozen over but filled mainly with Sangamon River water. The Quiver

Creek, tributary of Quiver Lake, is reported to have shown 11.9 to 12.3 of oxygen, and to have yielded in hoop nets put down over night vigor- ous and active European carp, native carp, or quill-back, buffalo, gars, channel cat, bullheads, black bass, striped bass and sheepshead, a good variety of ordinary fish in good condition.

Thus it will be noted that the fish which were in distress were oc- cupying polluted waters, and were apparently not affected by the unpolluted streams, even although the same were ice bound.

In this connection it should be noted, however, that in natural lakes and rivers, unpolluted by sewage, the exhaustion of oxygen and the distress of fishes may occur under the ice due to the decomposition of vegetable organisms. The distress of fish in the ice bound condition of the stream was observed upon the Illinois River prior to 1900. This situation may or may not have been brought about by sewage contamination.

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Future Effect of Water-Way Improvement.

When the Illinois water-way is built some changes will be brought about in the river conditions, principally between Lockport and LaSalle.

In this reach of the Des Plaines and Illinois Rivers it is proposed to improve the same on the basis of slack water navig'ation. To accompHsh this purpose dams will be constructed at Brandon Road, Dresden Island, Marseilles and Starved Rock. The pond created by each of these dams will extend to the foot of the next dam up-stream. At the present time the water occupies a period of about thirty- seven hours in its passage from Brandon bridge to LaSalle. Except for the pond created by the present Marseilles dam the current is rapid and conditions are favorable for the absorption of atmospheric oxygen. After the construction of the water-way based on present plans, contemplating a flow of about 10,000 second feet, the time of travel between Joliet and LaSalle will be increased to about 66 hours. The water surface area in this reach of the stream is about 10.5 square miles at the present time. The dams will increase it to about thirteen square miles.

Below LaSalle the flow of water is much less rapid. Six and one- half days is at present required for it to flow from LaSalle to Peoria.

The total time of flow from Joliet to the mouth of the Illinois River is about thirteen days at summer stages with present flows. With the improved water-way assuming a flow of 10,000 second feet conditions below LaSalle will not be greatly changed. Proposed plans contemplate water surface elevations which differ not greatly from those prevailing at present. With this flow, however, the existing dams will probably be taken out.

Thus the net result of the construction of the water-way will be practically to double the time of travel from Joliet to LaSalle, and to increase the area of water surface about twenty-five percent. Below LaSalle conditions will remain about as at present.

Conditions with Smaller Diversions.

If the diversion of water from Lake Michigan is very much below 10,000 second feet the plan for the Illinois water-way will probably require the retention of the present dams below LaSalle. Above La- Salle the dams contemplated under a 10,000 second foot flow would probably be unchanged, and the existing areas would not be greatly al- tered as compared to the larger flow. The time of travel, however. :

38 would be increased approximately in an average ratio to the quantity of water flowing. Rough approximations of the time of travel, assuming various quantities flowing in the stream would be as follows

TIME OF TRAVEL IN DAYS.

Joliet LaSalle to to mouth of LaSalle Illinois River 10,000 feet per second 2.7 14.5 8,500 " " " 3.2 17 13 7,500 " " " 3.6 19 4,167 " " " 6.4 35 2,000 " " " 73

It is believed that the net effect of the construction of the water- way will be to introduce into the Illinois River a series of four ponds above LaSalle, which may be expected to have a similar effect to that now produced in Lake Peoria. It is believed that the net effect upon the stream under present pollution and diversion conditions would be to throw the "dead line" now existing near Peoria Lake much further upstream. 39

PART III POPULATION AND GROWTH.

Chicago has grown from a frontier trading post to the third city of the world within a period of ninety years. It is the commercial and transportation center of the largest and richest agricultural community on this continent. Its position is such, as regards lines of communica- tion, that it will continue to be the hub of interior America. Its future development must inevitably follow the development of a vast interior region, the limits of growth for which cannot be predicted. In planning sewage disposal works for this great industrial center, it obviously will be wise to plan for a larger future growth. It is not financially practicable, however, nor is it wise to build very far in advance of immediate requirements. It is practicable, however, to plan for future growth, and to build upon a unit system so that units may be built a little in advance of need. If the plan is wisely made each unit so built will be permanently useful. It will constitute a link in a future chain of sev/age disposal works. Thus each dollar invested will be a permanent investment. If the growth is more rapid than anticipated, units can be added more rapidly, and assessed valuations will be available to meet the necessary charges. If growth is less rapid than is anticipated, works constructed from year to year will be useful for a longer time.

Population—Sanitary District: The Sanitary District of Chicago includes fifty-two towns and villages lying within Cook County, Illinois. The population by 1920 census was 2,978,635, of which 2,701,705 or ninety-one percent was resident within the corporate limits of the City of Chicago. Table 5 is a statement of the population within the present boundaries of the Sani- tary District in the census 1900 to 1920 inclusive. Within this period the population of the district increased sixty-seven percent. The outlying towns and villages practically trebled in population during the two decades.

Greater Chicago Region:

Since 1900 municipal growth has extended beyond the Illinois bor- der line into Northern Indiana, in which a great industrial region is developing, served by numerous main lines of railroad and new lake .

40 harbors, which have been built at Gary and East Chicago. Improved labor conditions in the outlying localities, adjacent to Chicago, have favored the location of certain industries, on the borders of the city limits, and in certain cities outside of Cook County. The greater Chicago region, as defined by U. S. census, includes Cook, Kane, Du- Page, Lake and Will Counties in Illinois and Lake County in Indiana. The total population of this region was 3,521,789 in 1920. It had increased seventy-five percent in the two decades following 1900. Table 6 shows the population within this region for each county for the last three census years. As will be noted the Sanitary District of Chicago includes approximately eighty-five percent of the total population of the greater Chicago region.

TABLE 5

POPULATION OF CITIES AND VILLAGES IN THE SANITARY DISTRICT OF CHICAGO

Population Name 1900 1910 1920 943 1,881 5,841 14,150 6.114 8,043 11,424

Brookfield (village) 1,111 2,186 3,589 Burnham (village) 328 795 1,237

Chicago (city) , 1,698,575 2,185,283 2,701,705 Cicero (town) 16,310 14,557 44,995 DesPlaines (village) 1,666 2,348 3,451 Dolton (village) 1,229 1,869 2,076 Elmwood Park (village) 1,380 18,721 25,668 37,234 445 424 705 4,085 6,594 10,768 483 683 914 1,020 1,899 3,381 652 760 5,395 7,227 9,216 127

Hinsdale (village) (DuPage County) . . 2,578 2,451 3,975 336 881 1,188 3,969 5,282 6,526 730 1,131 1,684 951 1,483 2,564 4,532 8,033 12,072 2,592 4,806 7,147 564 836 1,079 190 276 1,441 514 569 1,258 ..

eon ceo 763 CCA Northbrook (Schermerville) (village).... 554

3,447 5,251 6,897 Oak Park (village) 19,444 39,858 Park Ridge (city) 1,340 2,009 3,383 679end l,9od-1 rtoo AO 94 < 558 917 1,166 River Forest (village) 1,539 2,456 4,358 River Grove (village) 333 418 484

Riverside (inc. N. Riverside) (village) . . 1,551 1,702 2,532 Riverview (village) 406 312 334 431 390 South Holland (portion village) 766 1,065 1,247 Stickney (village) 550 547 949 4,019 359 355 Western Springs (village) 662 905 1,258

West Hammond (Calumet City) (city) . . ^,9o5 4,948 7,492 2,300 4,943 7,814 Winnetka (village) 1,833 3,168 6,694

1,788,278 2,338,278 2,978,635 Total population, excluding Chicago. 89,703 152,995 276,930

TABLE 6

POPULATION OF THE CHICAGO METROPOLITAN DISTRICT

1900 1910 1920 County Census Census Census 1,838,735 2,405,233 3,053,017 78,792 91,862 99,499 28,196 33,432 42,120 34,504 55,058 74,285 Will 74,764 84,371 92,911 37,892 82,864 159,957

Total 2,092,883 2,752,820 3,521,789

Chicago Growth Compared to Other Cities: We show on Figure 11 a diagrammatic representation of the growth of Chicago with a comparison of the growth of London and

New York, the only cities which exceed it in population ; also several other cities. It will be observed that the rate of growth of Chicago has been exceeded only by that of New York, which has been largely influenced by annexations. Figure 12 is a similar diagram showing a little more clearly the growth of the Chicago region, as compared to 42

London and New York, the population of these two cities being platted for the several decades immediately before and after the time when they passed the three million mark, without regard to the year. Within the past ten years there have been several comprehensive studies of the future growth of Chicago and vicinity ; more particularly the studies for the Chicago Traction Commission, the Commission on Smoke Abatement and also several studies concerning the improvement of the Chicago Water Works. The Chicago Telephone Company necessarily keeps itself quite accurately informed as to the probable requirements for the extension of its service. It has recently made a study of the growth of the Chicago region.

YtAR Figure 11.—Population growth of Chicago and other large cities, with city- engineer's forecast for the city of Chicago. 43

All these investigations substantiate, with reasonable accuracy, the figures which have been prepared by the Sanitary District of Chi- cago, as representing the most probable future population of the Sani- tary District so far as it can be determined in the light of past growth and recent development in this region.

Forecast of the Sanitary District: We show diagrammatically on Figure 12 the forecast of the Sani- tary District for the population within the Sanitary District up to the year 1970. In designing sewage purification works it will be important

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Figure 12.—Population growth and forecast for the Sanitary District of Chicago and City of Chicago in comparison with growth of other large cities. (Dates refer to local population only). 1. Chicago only, Traction Co. forecast. 2. Chicago only, Assn. of Commerce Smoke Comm. forecast. *Note—Estimate of the Sanitary District of Chicago. Greater London population 3,000,000 in 1857. Greater New York population 3,000,000 in 1895. 44

2.000,000 D iaqram Showinq Population By Districts Estimate op 5anitarv District l,cioo,ooo of chicago To Accomporn^ R.cpor4- o-P \.8oo,ooo A\_VORD, &URD\CX;8cH0W50M

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to determine present and prospective populations by locality, as a basis for determining- the amount of sewage delivered to each plant. Table 7. shows the estimate of the Sanitary District for each future decade, divided as between five localities in which purification works will probably be required. Figure 13 shows the same facts diagrammatically. This diagram is chiefly useful in illustrating the comparative rates of growth in the different parts of the district, and in preparing approximate estimates of population for the years intermediate between the census years.

TABLE 7

PRESENT AND FUTURE POPULATION OF AREAS TRIBUTARY TO TREATMENT PLANTS, AS ESTIMATED BY THE SANITARY DISTRICT OF CHICAGO

Total North West all Year Side Side Calumet S. W. Side Misc. Plants 1920 590,000 1,300,000 160,000 850,000 100,000 3,000,000 1930 800,000 1,430,000 225,000 1,040,000 215,000 3,710,000

1935 915,000 1,490,000 255,000 1,135,000 275,000 . 4,070,000 1940 1,015,000 1,550,000 290,000 1,230,000 340,000 4,425,000 1950 1,230,000 1,680,000 350,000 1,415,000 465,000 5,140,000 1960 1,450,000 1,800,000 415,000 1,600,000 595,000 5,850,000 1970 1,670,000 1,920,000 480,000 1,780,000 730,000 6,580,000

Distribution of Population: We present herewith Figures 14 and 15 which show a diagrammatic representation of the distribution of the population of Chicago and

vicinity for the census year 1920, and the population distribution as it

will probably be in 1940. These diagrams were prepared by the Illi-

nois Bell Telephone Company ; each spot on the diagrams represents 100 families. These diagrams serve to indicate the most favorable locations for sewage purification works. As will be pointed out later the Sanitary District has apparently selected the most favorable sites possible for purification works, in that localities have been chosen as remote as possible from present and future habitation, with due regard to proximity to the districts contributing sewage. Figure H.—Map of Chicago showing distribution of population in 1920. Figure 15.—Map of Chicago showing distribution of population in 1940. 48

PART IV

AMOUNT AND QUALITY OF SEWAGE.

In a study of the sewage problem of any community, a knowledge of the volume and quality of the sewage is of primary importance. With respect to quality, sewages are often classified as domestic and industrial, and the use of these terms is generally intended to convey the idea that domestic sewage is that resulting from strictly domestic or household operations, while industrial sewage is that resulting from manufacturing or industrial operations. A strictly domestic sewage consists of the water-borne wastes resulting from household operations in the laundry, kitchen, bathroom, and toilet and the qualitative character of such wastes is substantially the same in any community where the habits of life of the people do not differ materially. Sewage of a strictly domestic character is rarely encountered in large cities, as most, if not all, of our large cities have more or less varied industries, which produce waterborne wastes differing in quality from strictly domestic sewage. The character and extent of industrial operations consequently are largely responsible for any wide differences in quality which may be found in the sewages of various cities.

Measurement of Load: Various analytical determinations are made today to give expression to the quality or composition of sewage, such as total nitrogen, free ammonia, suspended solids, settleable solids, oxygen absorbed from permanganate, stability value, biochemical oxygen demand, etc., and in the discussion of the quality of sewage, the only analytical value which will be used for the present will be that secured by the biochemical oxygen demand test. The biochemical oxygen demand test consists of incubating a known volume of sewage with known volumes of pure water containing a known supply of oxygen in solution, and observing the rate at which the oxygen is exhausted, also, the total amount of oxygen required to effect a complete combustion of the putrescible matter in the sewage.

The incubation is carried out at a constant temperature, usually twenty degrees C, and for a sufficient number of days to accomplish a practically complete destruction of the readily oxidizable material in the sew- 49 age. This test attempts to show what happens in the way of oxygen depletion in a stream of pure water when it is polkited with sewage.

It has long been known that streams are able to affect a destruction of putrescible matter and after doing so to recover their original purity.

When sewage is discharged into a stream of water there begins a drama with three actors, namely putrescible matter, bacteria and oxygen. Bacteria and oxygen combine to destroy putrescible matter, and if the bacteria have an ample supply of oxygen, putrescible matter is destroyed in a quiet and orderly manner, but if the supply of oxygen is inadequate, the drama may develop into a tragedy, and although the bacteria will eventually triumph, the stream will suffer considerably from the experience.

The problem then is one of oxygen supply, if sewage destruction is to be accomplished without offense, and there are a number of factors which govern the supply of and demand for oxygen in a polluted stream of water. One second foot of pure water at a temperature of 32° F. is saturated when it carries 79 pounds of oxygen in solution in a twenty- four hour period, whereas at a temperature of 86° F., it is saturated when it carries 41 pounds of oxygen in solution. On the other hand, the activity of the bacteria which destroy the putrescible matter, is almost nil at 32 degrees F., whereas at 86 degrees F., they are exceedingly active. It is thus apparent that in cold weather there is a large oxygen content in the water and a low rate of demand, whereas in warm weather there is a low oxygen content in the water and a high rate of demand.

R eaeration:

An additional factor in the recovery of a stream from pollution is that of reaeration, which is more rapid in warm weather than in cold, and also increases with the degree of depletion; i. e., if the water is saturated, there will be no reaeration, if it has a zero saturation, the reaeration will be at a maximum for any given condition, and the rate of reaeration will decrease as the oxygen deficit decreases. Other factors affecting reaeration are turbulence and depth, the replenishment increasing with the turbulence and decreasing with the depth.

Example of Oxygen Requirement: As a concrete example of the relation of the oxygen demand of a sewage and the oxygen supply of a stream, it will be assumed that one second foot of sewage per day, or a total of 646,000 gallons has, by the biochemical ox3^gen demand test, been shown to require 820 pounds of oxygen to destroy its putrescible matter, and, that it is desired to mix this second foot of sewage with enough second feet of saturated water so at 86 degrees F. to supply all the oxygen required. The one second foot of sewage per day require^ 820 pounds of oxygen and one second foot of water per day at 86 degrees F. will supply 41 pounds of oxygen, consequently twenty second feet of water will be required, neglecting, of course, reaeration.

Reaeration is no doubt a big contributor to the total oxygen re-

quired to destroy putrescible matter in a stream, but, as it has a value

which is a resultant of depth of water, turbulence, temperature, and

degree of depletion, it is difficult to give it quantitative expression. The efficacy of reaeration in preventing complete depletion of oxygen in a

stream is probably closely related to the excessive demand for oxygen which occurs during the early stages of the incubation of the sewage and stream water. The results of many studies of the oxygen demand of mixtures of pure water and sewage when incubated in closed containers, which prevent reaeration, have indicated that on the basis of the total amount of oxygen absorbed in twenty days at twenty degrees C, twenty-one per-

cent will be required the first day, sixteen percent the second day, thirteen percent the third day, eleven percent the fourt day and seven percent the fifth day, making a total of sixty-eight percent for the first five days. The second five days will require twenty-two percent of the total and the next ten days, ten percent of the total of which, however, but

three percent is required in the last five days.

These rates are indicative of a general average result rather than absolutely specific, and are given to show the need for a good supply of oxygen during the first few days of contact between sewage and stream water. In converting a given oxygen demand value secured by a given period of incubation, to an oxygen demand value for a longer or shorter period of incubation, the above rates of satisfaction have been used, as the results of experimental studies in many places have shown them to be reasonably reliable.

If the supply of oxygen, which the diluting water carries in solu-

tion, is insufficient to meet the needs of the wet combustion process which takes place in a polluted stream, reaeration conditions may be

such that the oxygen supplied in that way will be used up as fast as it

is absorbed and distributed and the water of the stream will be left in a condition of zero saturation. With these considerations in mind, a study of daily oxygen requirements of the sewage of the Sanitary District of Chicago has been made, and the results of this study are herewith presented. 51

Load of Sanitary District: There are two ways of expressing' the daily oxygen requirements, namely, as a definite number of pounds of oxygen per person per day, or, as a total number of pounds of, oxygen per day for the entire district. The determination of the total daily oxygen load from a representative district divided by the population contributing to this load, will give a per capita daily load which may be applied to the whole district. In the event that there are large industrial loads that have a marked effect on the total load, such industrial loads should be determined separately and added to the total load as estimated from the representative district, in which event, the human population per capita load will be increased, or, the industrial loads may be converted into an industrial equivalent population load, in which case the human population plus the industrial equivalent population times the human population per capita load will give the total load.

A common way of expressing an industrial load is to convert it into an equivalent human population, but in order to avoid confusion, no use has been made of the industrial equivalent population.

The sewage of the entire Sanitary District of Chicago is discharged by approximately 150 sewers, varying in diameter from two feet to sixteen feet, into the north and south branches of the Chicago River, the Des Plaines River, the Calumet River, and the Drainage Canal, making it very difficult to get an accurate determination of the sewage flow of the entire district.

Thirty-Ninth St. Studies 1914:

During the year 1914, hourly samples of sewage were taken at the 39th St. sewage pumping station, and dosed with nitrate solution of known concentration, then allowed to incubate for ten days. At the end of the ten-day period of incubation, the twenty-four hourly samples were composited without correction for flow fluctuations and the residual nitrite and nitrate determined on the composite sample. The oxygen demand value secured in this way was taken as the mean value for the day. The incubation was not carried out at a constant temperature, but at whatever temperature happened to exist where the incubating samples were stored. The average oxygen demand as determined in this manner after a ten-day incubation was found to be 121 parts per million, which means that 121 pounds of oxygen would be required to destroy the putrescible matter in one million pounds of sewage, or 1008 pounds of oxygen would be required for one million gallons of sewage. The average rate of pumpage was found to be 71 million gallons per day ( or *219 gals.

*Note—Total XDity pumpage year 1914, 2.54 g-als. per capita. 52 per capita), and this was secured by taking the daily records of the speed of the pumps and determining the discharge by using the manu- facturer's speed, capacity, and head curves. There is some doubt as to the accuracy of this method in determining the discharge of the pumps. The population of the district contributing sewage to this station was estimated at 324,000. On the basis of the above data the daily per capita oxygen load was 1008 pounds times 71 M. G., divided by v324,000 or 0.22 pounds of oxygen, on a ten-day oxygen demand basis.

Thirty-Ninth St. Studies, 1920:

Between November 8th, 1920, and December 11th, 1920, a similar investigation was made at the 39th St. sewage pumping station. The oxygen demand was determined by the dilution method after a ten-day incubation at a constant temperature of twenty degrees centigrade. Samples were taken hourly, with four consecutive hourly samples composited for a single oxygen demand test. Six composited samples per day w^ere subjected to the oxygen demand test, and the mean of the six values was taken as the daily mean value. No attempt was made to weight samples to conform with hourly flow fluctuations. The average oxygen demand after a ten-day incubation at 20 degrees C, was found to be 140 parts per million, which means that 1166 pounds of oxygen would be required to destroy the putrescible matter in one million gallons of sewage. The average rate of pumpage was found to be 86.17 million gallons per day ( or *207 gals, per capita), the same being estimated as in the previous test. The population was estimated to be 417600 and on the basis of the above data the daily per capita ox3^gen load was 1166 pounds times 86.17 M. G. divided by 417600 or 0.24 pounds of oxygen on a ten-day oxygen demand basis.

Des Plaines Studies: The operating results for the Des Plaines treatment works for the year 1924 show an average daily sewage flow of four million gallons, an average ten-day oxygen demand of 153 and a tributary population of 40000 and on the basis of the above data the daily per capita oxygen load was 153 pounds times 8.33 times 4 M. G. divided by 40000 or 0.127 pounds of oxygen on a ten day oxygen demand basis.

Calumet Studies: :

The operating results for the Calumet treatment works for the year 1924, show an average daily sewage flow of thirty million gallons, an average ten-day oxygen demand of eighty and a tributary population

*Note—Total city pumpage year 1920, 27G gals, per capita. 53 of 107,000, and on the basis of this data, the daily per capita oxygen load was 80 pounds times 8.33 times 30 M. G. divided by 107000 or 0.187 pounds of oxygen.

Comparison with Other Cities:

In Table 8, a comparison may be made between Chicago sewage and that of other American and English cities. It is quite apparent from the data contained in this table that Chicago sewage is considerably stronger than the average strength of sewages listed in the table.

Industrial Load:

The Chicago industrial load is quite large in the aggregate, the principal elements of which, in the order of their magnititde, are as

TABLE 8 TABLE SHOWING THE STRENGTH OF MUNICIPAL SEWAGES ON THE BASIS OF THE OXYGEN REQUIREMENT IN POUNDS PER CAPITA PER DAY Gallons sewage 5-Day Pounds per capita oxygen oxygen per day by demand required contributing in per capita Ref. City population P. P. M. per day 131 92 0.100 Baltimore, Md 106 120 0.106 Canton, Ohio 64 213 0.113 Columbus, Ohio 94 190 0.148 88 155 0.114 89 144 0.107 101 118 0.099 Rochester, N. Y 137 104 0.119 B Malton, Eng 40 467 0.155 C Huntingdon, Eng 27 475 0.107 D Brooklyn, N. Y 102 223 0.189 Min. value 0.099 Max. value 0.189 35 350 0.102 Strong Eng. Sewage 35 500 0.146 206 106 0.182 G Chicago 219 91 0.167 H Chicago 100 122 0.102 I Chicago 280 64 0.149

References: A. U. S. Public Health Service Bull., No. 132, p. 115. B. Eighth Report Roy. Com. Sew. Disp. Vol. 2, Appendix, pages 27, 68, 81.. C. Eighth Report Roy. Com. Sew. Disp. Vol. 2, Appendix, page 20. D. Brooklyn, N. Y. Sewage Treatment Experiments by George T. Hammond, Reprinted from 1919 Proc. Am. Soc. Mun. Improvements, p. 20 and 22 of Reprint. E. Eighth Rept. Roy. Com. Sew. Disp. Vol. 1, page 9. F. Operation data, 39th St. Sew. Pump. Sta. Year 1920. G. Operation data, 39th St. Sew. Pump. Sta. Year 1914. H. Operation data Des Plaines Sewage Treatment Works, Year 1924. I. Operation data Calumet Sewage Treatment Works Year 1924. . :

follows : Stockyards and Packingtown wastes, corn products wastes, tannery wastes, wool pulling and washing wastes, and numerous other

smaller industrial wastes, many of which are common to all large cities. The Stockyards and Packingtown wastes and the corn products wastes have been and are now being extensively studied by the sanitary engineering division of the Sanitary District and the conclusions which they have arrived at may be summarized as follows

Estimated average Average Pounds daily sewage flow 10-day oxy- oxygen in million gallons gen demand required for year 1925 value per day

Stockyards Avastes . . 33.5 900 250,000 Corn Products wastes 15.5 600 77,000 Total 49.0 327,000

The sewage flow from the packing industries is based on numerous sewer gagings and the oxygen demand is an average value of numer-

ous determinations made between the years 1911 and 1918, all of which

data is reported in detail in the Reports on Industrial Wastes from the

Stockyards and Packingtown, Vol. 1 having been issued in October, 1914, and Vol. 2 in January, 1921. The tannery and other miscellaneous wastes of the Sanitary Dis- trict of Chicago have been estimated by officials of the Sanitary District to have a daily oxygen requirement of 40,000 pounds. The total industrial load of the district has been estimated by officials of the Sanitary District to have a daily oxygen requirement of 367,000 pounds.

Canal Studies: An entirely separate study of the Chicago load has been made by investigations conducted at several points along the canal between

Brandon Bridge below Joliet, and Summit. In these studies the load was estimated by determining the oxygen lost from the mixture of lake water and sewage to a given station or observation point, and adding this load to the unsatisfied demand at the station. The sewage flow was an assumed value, the dissolved oxygen content of the sewage was assumed, the dissolved oxygen content of the diluting water was determined by analysis, the total flow of the canal was taken from a rating

curve for a U. S. G. S. gaging station, and all other values were determined by analysis. The results of these studies as well as all other studies of the Chicago load, which have been investigated, are recorded in Table 10. : .

An inspection of the data in Table 10 shows that the daily oxygen load as estimated from the results of canal studies varies as follows

1. On basis of 5 day oxygen demand— 886000 to 1195000 pounds 2. On basis of 10 day oxygen demand—1117000 to 1580000 pounds 3. On basis of 20 day oxygen demand— 1266000 to 1760000 pounds

TABLE 9. SHOWING INDICATED TOTAL OXYGEN LOAD BASED ON LOCKPORT DATA.

July August Febr'y 1922 1922 1922

Temp, lake water, degrees C* (temp.) 22.4 23.8 1.0

Oxygen in lake water, P. P.M.* (ave.) : . . 8.45 7.88 12.37 Oxygen found at Lockport in P.P.M 0.01 0.01 9.11 8.44 7.87 3.26 Total flow in second feet 8696 8360 8330 Assumed sewage flow in sec. ft 1220 1220 1220 Dilution factor at Lockport 7.1 6.85 6.8 B.O.D. value reduction to Lockport (in 1220 sec. ft.) 60 54 22 B.O.D. value at Lockport—5 day value 11.20 11.88 23.46 B.O.D. value at Lockport, corrected to 1220 sec. ft.— 5 day value 80 81 160 Total B.O.D. value at sewer outlets-5 day value 140 135 182 Total daily oxygen load in pounds 919,000 886,000 1,195,000

*Average9 found to prevail in these calendar months.

A further inspection of this table will show that the average daily oxygen load of studies Nos. 7, 8, 9, and 10 (warm weather period) based on the 20-day demand values, is 1,300,000 pounds and that the average daily load of studies Nos. 5 and 6 (cold weather period) based on the 20-day demand values, is 1,600,000 pounds. In view of the fact that there was a marked oxygen depletion at the points of observation during the warm weather tests, and probably a considerable amount of replenished oxygen used in satisfying the demand up to the observation station, and that this condition did not obtain to such a marked degree in the cold weather tests, it seems probable that the total indicated load of 1,600,000 pounds of oxygen is more nearly correct for the year 1922. The average daily oxygen load based on the 10 day oxygen demand values and the cold weather tests is 1,450,000 pounds and the average daily oxygen load based on the 5-day oxygen demand values and the cold 56

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57 weather tests is 1,092,000 pounds. Taking human population for 1922 as 3,100,000, the oxygen load per capita per day was as follows On basis of 20-day demand value 0.516 On basis of 10-day demand value 0.468 On basis of 5-day demand value 0.352

Taking the human population for 1925 as 3,355,000, the total oxygen load per day for the year 1925, would be as follows On basis of 20-day demand value .... 1,730,000 pounds On basis of 10-day demand value. ... 1,570,000 pounds On basis of 5-day demand value. ... 1,180,000 pounds

Resume of Studies: In Table 11 are shown comparative data on the oxygen requirements of the sewage of the Sanitary District of Chicago, as determined from three separate sources. In the studies conducted by the U. S. PubHc Health Service during the year 1922, samples were taken from the canal at Lockport between

6 a. m. and 8 a. m., and the oxygen demand determined after a 5-day period of incubation at a constant temperature of twenty degrees C. These studies were completed in August, 1922, and some doubt existed as to the single samples being representative. The Sanitary District of Chicago was asked to make a study which would show whether there was a fluctuation in strength during a twenty-four hour period. A study to determine this was made by the Sanitary District during September, October, and November, 1922, samples being taken at the same sampling point at Lockport as that from which the U. S. P. H. S. samples were taken, and at 4 a. m., 8 a. m., noon, 4 p. m., 8 p. m., and 12 p. m. daily. The oxygen demand was determined on each sample by a 5-day incubation at a constant temperature of 20 degrees C A curve was plotted showing the daily fluctuations at four hour intervals and another curve was plotted to show the fluctuations of the flow during this period. From these two curves a correction factor of

1.27 was evolved to apply to the single daily sample taken from 6 a. m. to 8 a. m. to make the oxygen demand representative. An hourly fluctuation curve for oxygen demand resulting from the temperatures obtaining in the canal water in September, October, and November will probably be different from a similarly plotted curve for warmer or colder it is believed that this weather ; consequently particular oxygen demand curve is not suitable or reliable for full year application. The load value secured in this way is less convincing than it would be had the results been based on weighted daily composites, and it is impossible to say whether the indicated load is too high or too low. 58

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The determination of the daily load from the results of the operation of the Calumet and Des Plaines sewage treatment works for the year 1924, would be open to criticism because the use of a per capita value secured from these results would result in adopting a load value from about three percent of the population of the district and calling it representative.

Best Criterion for Domestic Load: The determination of the daily domestic load from the results of the 1920 studies of the 39th Street sewer seems at this time to be the most logical course to pursue for the following reasons 1st. The district contributing to this sewer is considered to be reasonably representative. 2nd. The study was made during a census year and for this reason a reasonably accurate estimate of the contributing population could be made.

3rd. The analytical data is complete and satisfactory for use in determining the load.

4th. The pumpage record is not thought to be very accurate and the average daily flow, if in error, is believed to be too high, and if this is true the indicated load is too high and the error is on the side of safety.

5th. The population contributing to this sewer is approximately ten percent of the total population of 'the district.

From the data which has been reviewed, it is thought that the load values as shown in Table 11 for the 39th Street sewer are the most dependable. Furthermore, it is thought that a carefully planned study of the canal at Lockport or at some other location or locations would result in a more reliable determination of the daily load, and these studies would also provide a check on the previous studies of the Stock- yards and Corn Products wastes.

Summarized Conclusions on 1925 and Projected Daily Loads:

In estimating the total daily load of the entire Sanitary District for the year 1925, and projecting these loads at five year intervals to 1945, the following basic data have been accepted and used

1. The 1920 results at the 39th St. sewer which show the daily domestic load to be 0.24 pounds of oxygen per capita per day on a ten- day oxygen demand basis. 2. The human population estimates of the Sanitary District for five-year intervals from 1925 to 1945.

3. A value of 900 for ten-day oxygen demand for the packing and stockyards industrial wastes, and the assumption that the strength 60 of this waste will not change materially during the period of time involved. 4. The estimate of the Sanitary District relative to the present daily volume of the Packingtown and Stockyards wastes for the years 1925 and 1945, which volumes are respectively thirty-three and one-half and 40 million gallons per day. 5. A value of 600 for the ten-day oxygen demand for the corn products wastes and the assumption that the strength of this waste will not change materially during the period of time involved.

6. The estimate of the Sanitary District relative to the present daily volume of the corn products wastes for the years 1925 and 1945 which volumes are respectively 15 and 19 milHon gallons per day. The oxygen demand values for the Packingtown and corn products wastes are accepted after a study of the many analyses, which have been made over a period of years. The actually determined value for the

Dav5 of Incubation at2o°c.

* G. L. Fugate, Eng. News-Record 94, No. 11.

t Data by Sanitary District of Chicago.

Figure 16—Biochemical oxygen demand based on various periods

of incubation. :

61 packing wastes is 900 parts per million for ten-days at 20 degrees C The value of 680 for the five-day demand at 20 degrees C; is a calculated value which was furnished from the laboratory of the Sanitary District. The twenty-day value was secured by dividing the ten-day value by 0.90. The basis for determining the load from the corn products plant was a determined five-day oxygen demand value of 450 and a calculated ten-day value of 600, both values being furnished from the laboratory of the Sanitary District. The twenty-day value was secured by dividing the ten-day value by 0.90. The basis for determining the domestic load was the determined ten-day oxygen demand value of 140 for the 39th St. sewer in 1920. The five day and twenty-day values were calculated by using a rate of satisfaction as follows: 5-day value 68% of 20-day value 10-day value 90% of 20-day value 20-day value 100% of 20-day value A curve of oxygen demand for packing wastes of Chicago and Houston, Texas, corn products wastes of Chicago, and 39th St. sewage of Chicago accompanies this report.

Table 12 contains a summary of the estimated daily oxygen loads of the domestic sewage, stockyards waste, and corn products waste, the sum of which is taken as the total daily load of the entire district.

It will be noted in this table that the total daily load is shown on the basis of 5, 10, and 20 day demand values, the 20-day value indicating what might be termed a substantially complete oxygen requirement, although it is not strictly an absolute value.

Although the total load as indicated by the 20-day value must be disposed of finally, it is not required that this amount of oxygen must be supplied as an initial content in lake water, as reaeration may be expected to contribute a substantial portion of the total oxygen required. The rate of oxygen satisfaction occurring from the beginning to the completion of a 20-day period of incubation in closed containers, which has been referred to previously in this discussion, has been found by a number of investigators to be reasonably reliable on a general average basis. These rates of oxygen satisfaction grouped for five-day intervals indicate the following period rates

1st. 5 days—68% of 20-day requirement 2nd. 5 days—22% of 20-day requirement 3rd. 5 days— 7% of 20-day requirement 4th. 5 days— 3% of 20-day requirement 62

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The above rates indicate that the demand for oxygen during the first quarter of the 20-day period is quite high and a substantial percentage of the total required for a reasonably complete destruction of the polluting material. The first 5-day period is also one in which poor reaeration conditions would be most apt to cause serious conditions in a stream through oxygen depletion resulting from a rapid rate of demand and a slow rate of replenishment. A study of the daily rates within the first 5 days shows that approximately fifty-five per cent of the total 5-day requirement must be met during the first two days. Quite a number of laboratory studies of mixtures of sewage and clean water incubated in open containers have shown invariably that where a proper dilution was used and in which enough initial oxygen was present to supply the needs for the first two days, an increase in dissolved oxygen content began after the first two days of incubation.

Criterion for Load: In view of such evidence as has been available and on the basis of the observed behavior of mixtures of sewage and clean water which have been shown to have reasonably definite general average rates of demand for oxygen, it is considered that a supply of dilution water having an initial oxygen content equal to the total 5-day oxygen demand load of the Sanitary District will be sufficient and satisfactory. For the above reasons, and for the reasons more fully stated in Part V and Part VI, we conclude that the 5-day biochemical oxygen demand of the sewage, and purification plant effluents, will furnish the most useful criterion of organic load. :

PART V. STANDARD OF MAXIMUM POLLUTION

It is desirable that a standard should be fixed to measure the eflPec- tiveness of means to be taken to prevent excessive pollution of the rivers below Joliet. This standard should be applicable whether the protective measures consist of dilution from Lake Michigan, sewage treatment works, or both. It will be most desirably and conveniently applied at the foot of the Drainage Canal. A test must cover a period sufficiently long to represent conditions which might create a nuisance, to eliminate unavoidable errors in sampling, and to average up ordinary variations that might be caused by excessive discharge frorri the storm sewers.

It is regarded as essential that the standard should exclude settle-

able suspended matters of an organic character ; otherwise deposits in the stream below Lockport, in the colder weather, will tend to rob the stream of oxygen in summer, thus producing undesirable conditions, the magnitude of which is not subject to prediction.

Subject to the above requirement, it is believed to be practicable to prescribe an oxygen content and an organic load, which, aided by reaeration and added dilution from streams below Lockport, will permit of satisfactory stream conditions at all places on the Illinois and Des Plaines Rivers, including freedom from nuisance, conditions tolerable for fishes in the Des Plaines and Upper Illinois, and such as to permit a thriving fish fife in the lower Illinois.

Limitations of Standard: In fixing a standard to be used as a governing basis for the pollution of the Illinois River, both now and hereafter, there are two considerations that should be set forth clearly in the beginning

1st. It is economically impractical to expect that the IlHnois River should be returned to a condition such as exists in streams which receive no pollution at all ; i. e., to a condition of pristine purity. 2nd. The existence of any appreciable amount of settleable putrescible material in the drainage course is apt to upset all eflforts which are aimed at the maintenance of proper stream conditions through sewage treatment and regulated diversion. 65

During the year 1922, the U. S. Public Health Service made a careful and systematic study of the condition of the waters of the Illinois

River and its tributaries.

Condition of Illinois River: The condition of the Illinois River was studied by taking daily samples of the water at a number of stations between Lockport and Kampsville and determining the dissolved oxygen and the five-day oxygen demand at twenty degrees C, in addition to other determinations the results of which will not be considered in this connection. The average monthly oxygen values for each sampling station are plotted on

Figures 5, 6, 7 and 8 to show winter, spring, summer and fall conditions in the Illinois River. An inspection of Figure 7 shows that during the winter months of the year 1922, there was a marked preponderance of oxygen demand over the dissolved oxygen supply at Lockport, and that a balance of oxygen supply and demand was not reached for a distance of approximately 50 miles below Lockport. The dissolved oxygen content of the water was, however, at no time or place below 7 parts per million, indicating that a low rate of oxygen depletion was taking place and that an absence of a smell nuisance existed.

An inspection of Figure 8 will show that during the spring- months of the year, the same disparity between oxygen demand and supply existed at Lockport, and that the balance was reached in April 29 miles below, in May 100 miles below, and in June 120 miles below Lockport. The dissolved oxygen in April was not below three and three-fourths parts per million, in May it reached a low value of one- half of a part, and in June it was zero at Lockport.

Figure 5 shows the summer conditions in the river and the oxygen values indicate that the Illinois River was practically dead for a distance of 113 miles below Lockport, from which point its condition began to improve until an oxygen balance existed at a distance of 125 miles below Lockport.

An inspection of Figure 6 shows conditions quite similar to those which existed during the spring months with a progressive improvement from September to November. The oxygen balance was established within the following distances below Lockport ; in Septem- ber, 122 miles ; in October, 92 miles, and in November, 52 miles, the improvement in the last month resulting both from an increase in dilution and a reduction in temperature. 66

Condition of Tributaries to Illinois River:

The condition of the waters of the tributaries of the IlHnois is reflected by their dissolved oxygen content and the demand for oxygen when incubated in closed containers for 5 days at 20 degrees C, and these values are recorded in Table 13.

The values recorded in Table 13 are the mean values for the months indicated, and are based on from ten to fifteen samples per month for each stream so that the information thus secured gives a very satisfactory index of the sanitary quality of the water. It will be noted from these monthly averages that in only three instances did the 5-day oxygen demand exceed the dissolved oxygen content, and the average relation for all the streams was: dissolved

oxygen, 2.9, oxygen demand 1.0, indicating a very safe relation between the oxygen supply and demand. The best condition found among the several tributaries of the Illinois was the average result for the Kankakee River, where the relation was 4.7 dissolved oxygen to 1.0 of oxygen demand.

A relationship for the Illinois River such as the average relation-

ship for its tributaries, we consider to be too severe and one which it would be impractical to impose because the cost involved would probably be out of proportion to the advantages which would accrue therefrom.

Seasonable Dilutions:

It is a well known fact that a given dilution will be more potent in preventing a nuisance in a polluted stream in cold weather than the

same dilution will be in warm weather, and this is due to the inhibiting effect of low temperatures on bacterial activity, and this in turn reduces quite materially the rate at which oxygen must be supplied. The danger of oxygen depletion in a polluted stream where a given

dilution prevails, is very materially reduced with the coming of freezing temperatures, consequently quite a material reduction in diversion water can be made during periods of low temperatures. Sufficiently reliable

information is not available at this time upon which to base a schedule of diversions which might be applied to take advantage of the changing rates of oxygen satisfaction which accompany marked changes in temperature. An indication of the effect of temperature on the rate of oxygen

depletion is shown by the results of some laboratory studies conducted at the sewage treatment works of Columbus, Ohio, some years ago, in which mixtures of sewage and clean water were incubated in closed containers for a period of twenty-four hours at various temperatures. 67 o11.

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The results of these studies showed the following rates of depletion, takino- tlie rate at the hii^hcst temi)erature used (90 degrees F.) as 100 percent ; 90 degrees F. 100 percent ; 80 degrees F. 76 percent ; 70 degrees F. 55 percent ; 60 degrees F. 38 percent ; 50 degrees F. 22 percent and 40 degrees F., 9 percent. If the above rates of oxygen depletion are typical of what occurs in the drainage course, it is evident that a very marked reduction in diversion water could be made during freezing weather ; also a schedule of seasonal diversions might be worked out which would materially reduce the total annual diversion required to meet the necessary sanitary considerations.

Oxygen in Lake Walter: In connection with the possibilities of regulated diversion to conform to temperature conditions and also to take advantage of the greater amounts of dissolved oxygen which are present in cold water, the following table of typical average monthly temperatures and dissolved oxygen content of lake water is of interest. The values given are mean monthly averages based on daily analyses of lake water at the 39th St. Pumping Station from September, 1921, through August, 1923.

Temp. Dissolved Oxygen Content Month Degs. C. Parts per Million

January 2.5 13.48 February 2.5 13.17 March 3.7 12.98 April 8.6 11.72 May 12.4 10.59 June 17.4 9.28 July 20.2 8.10 August 21.5 7.80 September 19.2 9.08 October 14.2 9.55 November 8.6 10.97 December 4.3 12.31

Annual Mean 11.3 10.75

Stability Studies:

The results of many years of river inspection studies at Columbus, Ohio, have shown certain relationships which exist between oxygen demand, dissolved oxygen, and stability as determined by the methylene blue test. Some of these relations are indicated in the following data: :

Range in oxy- Ave. Oxy. de- Average dis- Per cent dis- Stability gen demand mand value solved oxy- solved oxy- value of values, 37 deg. within the gen in water gen is of oxy- water as P 94. hrc in ciifn gen demand taken in situ

25-30 27.5 0.00 0.00 3 20-25 22.0 0.00 0.00 3 15-20 17.0 0.34 2.00 5 10-15 12.1 2.16 18.00 36 7-9 8.0 2.07 26.00 62 Below 7 4.4 3.92 89.00 84

A study of individual samples having oxygen demand values between 6 and 12 and showing complete stability by the methylene blue test, has indicated that the dissolved oxygen does not have to equal the oxygen demand value to insure complete stability, and a few instances have been noted where the dissolved oxygen in the river water was only forty percent of the oxygen demand yet the samples showed complete stability, indicating that some other source of oxygen was available, probably in the form of nitrites or nitrates. Five-Day Value: As the relationship between the rapidity of oxidation in sewage at constant temperature is subject to prediction, approximately from day to day, it would be possible to use any reasonable period of incubation as a test citerion. The period of five days has been frequently used in determining the quality of sewage and sewage polluted waters. It has the advantage over other periods of incubation in that if a mixture of sewage and water contains sufficient oxygen to meet the five day oxygen demand of the organic matter content, then the liquid under ordinary conditions in streams will not become entirely devoid of oxygen, and thus no nuisance will be created. If a shorter period of incubation should be used as a criterion, the oxygen content for equal freedom from nuisance would necessarily exceed the biochemical oxygen demand. If a period of incubation longer than five days should be taken, an oxyben content less than the biochemical oxygen demand would be justified. Therefore, the use of the period five days as an index is a con- venient period for use. It has been used by the U. S. Public Health

Service in its stream studies in the United States, and it was adopted by the Royal Commission on Sewage Disposal in its very comprehensive report upon "The Sewage Pollution of Streams" in England. Laboratory Experiments Certain laboratory experiments at Columbus, Ohio, in connection with the sewage disposal problem, bear upon this point. Table 14 shows certain data regarding the rapidity of oxygen depletion and the recovery thereof with sewage in open containers. . .. : 70

In the first two columns of this table it is apparent that all of the oxygen absorbed from the air was used up at once and this continued for six days in both the first and second tests. In the third test it was five days before the original content of oxygen was restored, and in the fourth test it was four days before this condition obtained. The last three tests were made on diluted samples, and the results indicate that the maximum depletion occurred during the first two days, and that thereafter reaeration and demand were balanced. The last three tests also show that the dissolved oxygen is drawn upon rather heavily before reaeration becomes a marked factor, indicating that if a marked depletion of dissolved oxygen is to be prevented the initial oxygen must be considerably in excess of the two-day demand. Reference in again made to the rates of satisfaction (page 50 of this report) which is as follows In 1 day—21% of total 20-day requirement In 2 days—37% of total 20-day requirement In 3 days—50% of total 20-day requirement In 4 days—61% of total 20-day requirement In 5 days—68% of total 20-day requirement

TABLE 14. RESULTS OF OPEN INCUBATION TESTS OF RAW SEWAGE AND TANK EFFLUENTS AT THE SEWAGE TREATMENT WORKS AT COLUMBUS, OHIO.

Dissolved Oxygen Content in Parts per Million of 10 Gallon Mixtures After Incubation in Open Containers at Room Temperature.

(1) (2) (3)

At Start . 1.0 0.0 1.2 1.2 5.3 6.8 6.9 After 1 day 0.0 0.0 0.6 0.6 0.8 2.4 3.2

After 2 days. . 0.0 0.0 0.3 0.7 0.7 3.2 3.2

After 3 days. . 0.0 0.0 0.4 1.0 1.1 3.6 4.0

After 4 days. . 0.0 0.0 0.7 1.6 0.8 4.0 4.0

After 5 days . . 0.0 0.0 1.5 2.8 1.0 4.0 4.3

After 6 days . . 0.4 0.4 2.6 3.0 1.0 3.9 4.0

After 7 days . . 0.9 3.5

After 8 days. . 1.0 3.8

After 9 days . . 1.2 4.0

After 10 days . 1.4 4.0

1. Raw sewage one volume, clean water 3 volumes. 2. Raw sewage one volume, clean water 7 volumes. 3. Raw sewage one volume, clean water 11 volumes. : :

If the 5-day demand is taken as the total oxygen which must be supplied by the dilution water, the relation is as follows

Per cent of Per cent of 20 day demand 5 day demand

One day 21 30.9 Two days 37 54.4 Three days 50 73.5 Four days 61 89.7 Five days 68 100.0

Reaeration Absent:

The standard hereinafter proposed in this report is that the residual dissolved oxygen and 5-day demand must be equivalent at Lock- port, and the worst condition that might result is shown in the following table, and is based on the entire absence of reaeration

Dissolved Oxygen in P.P.IVI. Initial Consumed Residual

Start 8.0 After 1 day 2.47 5.53 After 2 days 4.35 3.65 After 3 days. 5.88 2.12 After 4 days 6.18 1.82 After 5 days 8.00 0.00

In the above table it is assumed that the dissolved oxygen content of the water is 8.0 parts per million, and complying with the standard proposed in this report, the 5-day demand would be 8.0 parts per million.

Reaeration:

It is our belief that there will be enough reaeration to prevent a serious depletion of oxygen in the Drainage Canal if the recommended standard of pollution is adhered to.

When the mixed lake water and sewage reaches Lockport, in summer, the purifying action of the lake water is finished. The oxygen content of the liquid is practically zero. Nevertheless in its further flow to Chillicothe, the total organic units, passing that point in a given time, are greatly reduced through agencies other than Lake Michigan water. This, notwithstanding the fact that the normal load in the summer season is greatly augmented by river bottom deposits which have remained in refrigeration during the colder months. 72

An analysis of the studies of the U. S. P. H. Service for the month of August, 1922, indicate that the purifying agencies acting below Lockport and above Chillicothe, from sources other than Lake Michigan, are more potent in total than the total diluting water from Lake Michigan. These purifying agencies may include sedimentation, putrefaction, and oxidation. In our opinion oxidation is the chief factor. This opinion is reinforced by the fact that between Chillicothe and Peoria (in Peoria Lake) a distance of sixteen miles, the recovery of

oxygen units in the water is nearly as great as was obtained in total diversion from Lake Michigan. In addition to the natural agencies' there are artificial agencies that

may be called into action if needed to increase reaeration namely, the ; fall at Lockport, and the available fall at the several state dams when

the Illinois waterway is built. Several studies of the river indicate a marked recovery in oxygen at the Marseilles dam where much of the

water is wasted over the dam. At Lockport it nearly all passes through the water wheels of the Sanitary District, with practically no oxygen gain at present.

Thus in our opinion reaeration even of still water is a most important agency of purification.

Dilution in Other Cities:

Attention is further invited to Table 15 which shows the dilution water available for several American cities which discharge untreated sewage into the streams along which they are located. The data contained in this table simply shows what has been allowed to exist as a permissible pollution and probably the conditions created therefrom in the several streams have varied from satisfactory to doubtful. The recommended standard contained in this report (eliminating

for the moment the matter of settleable solids) is that 5.9 cubic feet per second per 1000 human population will be required to properly dispose of the entire untreated sewage of the Sanitary District of Chicago during the warm weather season of the year.

Dilution After Purification: We show in Table 16 a Hst of cities in which more or less complete purification has been adopted, together with the amount of diluting

water that is available in dry weather to mix with the purified effluent in the stream below the purification works. The dilution is expressed in cubic feet per second per thousand of population based on the 1920 census. It will be observed that in several instances the stream goes dry. 73

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The numerical average dilution is .58 second feet per thousand people. The weighted average is .42 second feet per thousand people.

Attention is called to the fact that as these cities grow the dilution ratio must become less, for in all cases, so far as known, there is no practicable means by which the dry weather flow of the stream will be increased. As compared to the above figures the standard recommended in this report and the recommended purification works contemplate dilu-

tions as follows : These dilutions are expressed in second feet of diluting water per thousand people as of the year 1935, when recommended sewage works have been completed, and ten years thereafter.

With total diversion including In Year In Year dilution water and sewage of 1935 1945

4,167 second feet 65 .5

6,000 second feet 1.1 .9 7,500 second feet. 1.5 1.2 8,500 second feet 1.7 1.4 10,000 second feet 2.1 1.7

These figures when compared with the data shown in Table 16 tend to indicate that a liberal amount of dilution is provided by the recommended standard for pollution and the recommended works for purification. It would appear that if this dilution is not sufficient, then the satisfactory disposal of sewage in many of our inland cities is impossible.

Pollution and Fishes:

It is evidently desirable that our streams insofar as possible should be sufficiently pure to permit the continuance of the natural water life thereof, including the fishes. This matter is particularly important in Illinois River which has been the best fish stream, in the Middle West.

For many years it has supported a commercial fishery with a catch ranging from ten million to twenty-three million pounds per year. About seventy-five percent "of the catch has been the so-called coarser fishes such as Carp and Buffalo. The so-called game fishes have been present in large numbers, and the Illinois River has been the playground of the game fisherman, and is so at present in its lower reaches. Of recent years the commercial catch has materially declined due in part to causes other than sewage pollution. Inorganic Wastes:

^ In certain parts of the country inorganic wastes are produced by industries that have poisoned the fishes and entirely destroyed them throughout long stretches of streams. Numerous industrial wastes are poisonous to fishes when present in certain amounts. 75

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Upon the Illinois River, so far as we know, the inorganic pollution has not reached amounts to be seriously detrimental to fishes.

Organic Pollution:

Certain of the coarser fishes may live and possibly thrive in waters more or less heavily sewage polluted. There is, however, a limit to the suspended organic matters present in waters in which fishes may maintain healthy conditions. All the fishes and the attendant train of water life necessary for their existence are killed, if the air supply in the water is reduced to zero for a sufficient period. This exhaustion of air may ^ result from, the decomposition of organic matters. With a reduction in the dissolved oxygen carried by a stream, the more sensitive fishes, and ultimately all the fishes endeavor to get away.

If escape is impossible they die. Some of the so-called coarser fishes may tolerate for a time, conditions in which oxygen is practically exhausted from the water, due to their power to take, store, and use a certain amount of atmospheric oxygen. Other fishes do not have this ability.

During the winter of 1924-5, ice conditions on the Illinois River reduced the dissolved oxygen to figures as low as from .4 to 1.8 parts per million. Under conditions such as this all kinds of fish taken from nets under the ice were found to be dead. At another place where the water contained 2.5 parts per million of dissolved oxygen, only Carp, Buffalo, and Gars were taken alive, all in a stupid condition. In another part of the stream where the oxygen content was 5.4 to 5.8, all fish were found in good condition under the ice.

It is believed that the above figures typify minimum conditions under which the fishes may survive. They probably require more favorable conditions than this throughout most of the year, in order to pro- pagate and thrive. A study of the graphs and tables of pollution on the Des Plaines and IlHnois Rivers herein-elsewhere shown, coupled with a knowledge of the places where fishes may now be found, throw some light upon limits of pollution. Fishing conditions below Peoria in general are good. Above

Peoria fishes are practically extinct except as follows : In seasons of low flow from the tributary streams, the dead line has moved downstream to Peoria and unfavorable conditions have been noted as far south as Havana. In seasons of maximum flow from the tributaries, the dead line moved upstream. It is understood that the 1925 season finds fishes in Peoria Lake, from which they have been largely or en- :

tirely absent for several years. This is probably due to the heavy summer flows in 1924. The study of the river seems to indicate that where the dissolved oxygen exceeds the five-day demand of the organic matter in summer, and considerably exceeds it throughout the remainder of the year that fish may thrive providing that the minimum dissolved oxygen at any time is three parts per million or more. In the works which we have suggested for sewage treatment at Chicago under various rates of dilution, and the standard herein-elsewhere set down for the liquid discharged by the Drainage Canal at Lockport, we believe that satisfactory fish conditions will be maintained throughout the greater part of the Illinois River. We believe that conditions will permit the coarser fishes to live at all places from Joliet to the Mississippi.

Recommended Standard:

After reviewing all the data which has been available relative to the past conditions which have prevailed in the Illinois River below Lockport, in addition to the studies which have been made and which indicate the sanitary quality of the waters of the streams which are trib-

utary to the Illinois ; and, with the purpose in view of seeking a reasonable degree of cleanness in the Illinois River below the terminus of the

drainage canal ; and, in the belief that the maintenance of such condition is not prohibitive in cost or unduly difficult of attainment ; the following standards of maximum pollution are proposed The liquid discharged by the Drainage Canal, as evidenced by the average of representative samples taken for any thirty consecutive days shall: (a) Be practically free from settleable solids deposited in two hours and

(b) Shall contain dissolved oxygen equal to, or exceeding, the biochemical oxygen demand of said Hquid for five days when incubated at twenty degrees Centigrade. (c) Shall contain not less than three parts per million of dissolved oxygen. In connection with the second standard relating to the oxygen balance, it is expected that there will be times when a condition of extreme refrigeration will exist in the waters of the canal which may result in a five-day oxygen demand value in excess of the dissolved oxygen content, but it is considered that, with an absence of settleable, putrescible solids in the water and the probability of the presence also of an ample supply of dissolved oxygen, a violation of this standard under these conditions 78 will not be detrimental to the maintenance of proper stream conditions in the Illinois River below the terminus of the Drainage Canal.

It is also suggested in connection with the application of these standards of permissible pollution that sewage treatment devices should not be expected to register maximum efficiency at all times, and that occasionally conditions will arise which will temporarily reduce their efficiency until proper corrective measures can be applied. Fallibility is characteristic of all things human, so that these standards are to be considered, as a rule, with occasional justifiable and unavoidable ex- ceptions. 79

PART VI. REQUIRED DEGREE OF PURIFICATION WITH VARIOUS DILUTIONS.

Our instructions require that we should report upon the purification works necessary under each of several diversions from Lake Michi- gan namely 8,500, and 10,.000 cubic feet per ; 2,000, 4,167, 6,000, 7,500, second. We have been instructed to consider these quantities as stated to be total diversions from the lake, including the water contained in the sewage plus the water used for diluting purposes. Thus practically speaking, the total diversion is equivalent to the dry weather flow discharged at the mouth of the Drainage Canal near Lockport.

Water for Dilution: For the purpose of this study the amount of water available for dilution in the critical period of the year, July and August, is considered to be the total diversion less the liquid volume of sewage of the Sanitary

District. In this computation it will be assumed that the sewage liquid is substantially the same as that which was analyzed in determining the total organic load of the Sanitary District as summarized in Part IV of this report. In the estimates for purification works hereinafter made, the above total diversions from the lake are considered as constant from year to year. The organic load of the city as shown in Table 12 of Part IV must grow from year to year. Experience indicates that during the hot weather months the sewage has been delivered at the sewer outlets in a condition practically devoid of oxygen. Within ordinary variations in the supply of water per capita, this will probably continue to be the fact. Therefore, with a constant total diversion from the lake and an increase in organic load which is delivered at the sewer mouths devoid of oxygen, the available diluting water will progressively decrease with the growth of the city, and the effectiveness of works for purification must progressively increase as time goes on.

Organic Load and Dilution: The organic content of sewage for practical purposes must be determined at the point of deHvery of the sewers. At this point in warm weather more or less oxidation has already taken place. The analysis :

80 represents the organic content of that particular sewage which has passed through a certain history as regards amount of dilution and in other respects. If the water supply per capita has been less, the analysis would have shown a sewage somewhat stronger in organic load per capita, for less oxidation would have taken place enroute to the sewer outlet. If the water supply per capita had been greater, the analysis would have shown less organic matter per capita, or more dissolved oxygen in the sewage, possibly both.

It is believed that when considering such variations in the use of water per capita as may occur in Chicago, it will be immaterial whether the organic wastes of the city are diluted by water taken into the sewers through the faucet or by water mixed with the sewage at the sewer outlet. It is our opinion, therefore, that it will be logical and proper to take the organic load of the District at the time when the analyses were made ; to take the liquid volume of the sewage existing at the time when

the analyses were made ; to assume that all sewage is delivered to the stream devoid of oxygen ; to assume that the liquid volume of the sewage will increase in proportion to the increase in the organic load, namely, that the consumption of water per capita remains constant; and that the available diluting water will be the total diversion less the liquid sewage computed upon the basis as above. The Sanitary District has made a careful estimate of the total liquid load as of the year 1920 at 758 million gallons. This is equivalent to 253 gallons per capita. We have used the round number 250 gallons ])er capita in computing Table 17, which shows the total net dilution water available between 1925 and 1945 under the various specified total diversions from 2,000 to 10,000 second feet. The table also shows the available oxygen in the dilution water. These figures are used in Parts XIII, XIV, and XV of this report.

Necessary Puri-fication Plant Efficimcies

In selecting the type of treatment best adapted to supplement various rates of dilution, it is useful to estimate the average rate of purification that would be required to produce a satisfactory effluent. Upon the following pages we describe the method of calculation, and tabulate the principal results. The degree of purification of the combined wastes of the Sanitary District of Chicago which must be accomplished in order to make certain specified diversions effective in maintaining proper conditions in the rivers which receive the discharge of the Drainage Canal, is determined on the basis of the daily oxygen required by the entire liquid-borne wastes of the District, and the supply of oxygen furnished daily by any given diversion of lake water. —...

TABLE 17. ESTIMATED "NET DILUTION WATER" WITH VARIOUS "TOTAL DIVERSIONS" AND OXYGEN AVAILABLE FOR DILUTION IN JULY AND AUGUST. Year 1925 1930 1935 1940 1945 Estimated volume of sewage delivered to stream devoid of oxygen 1280 1410 1530 1650 1770

With 2000 sec. ft. Constant Diversion Net water for dilution sec. ft 720 590 470 350 230

Available oxygen lbs. per day. . . 31000 25400 20200 15000 9900 With 4167 sec. ft.Constant Diversion 2887 2757 2637 2517 2397

Available oxygen lbs. per day. . . 124000 118400 113200 108000 103000 With 6000 sec. ft. Constant Diversion Net water for dilution sec. ft 4720 4590 4470 4350 4230

Available oxygen lbs. per day. . . 203000 197000 192000 187000 182000

With 7500 sec. ft. Constant Diversion 6220 6090 5970 5850 5730

Available oxygen lbs. per day. . . 268000 262000 257000 252000 246000

With 8500 sec. ft. Constant Diversion Net water for dilution sec. ft 7220 7090 6970 6850 6730

Available oxygen lbs. per day. . . 310000 305000 300000 294500 289000

With 10000 sec. ft. Constant Diversion Net water for dilution sec. ft 8720 8590 8470 8350 8230

Available oxygen lbs. per day. . . 375000 370000 365000 360000 354000

The basic data for the first part of this computation is recorded in

Part IV, Table 12, in which is shown the total oxygen required per day, separately and collectively, by the three polluting elements contributing to the load. This same table also shows the total daily oxygen loads of the entire district for the year 1925, and for five-year intervals to 1945. One second foot of lake water per day during the warm months of the year (July and August) will supply forty-three pounds of oxygen, and the second feet of lake water required per day during July and August will be as shown in the first portion of Table 18. Taking, for instance, the second feet per day required for the year 1925, Table 12 of Part IV shows the total daily oxygen requiremnt on the five-day demand basis to be 856,000 pounds, consequently, 856- 000 pounds divided by forty-three pounds gives 19,900 as the second feet required per day for untreated sewage. Table 18 shows the daily oxygen loads for the polluting unit of each polluting element ; also the second feet of water required per day during July and August for each polluting unit. These months were selected for use because they represent the critical period of the year both as regards oxygen supply and demand. 82

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If it is desired to determine the pounds of oxygen available in one second foot of lake water per day, the result is secured by multiplying as follows Parts per million of dissolved oxygen in water X 0.646 M. G. in one second foot per day X 8.33 pounds per gallon, or parts per million of dissolved oxygen in water X 5.4. The factor 5.4 is the product of 0.646 X 8.33 and is a constant. Table 19 shows the second feet required per day during July and August for five-year periods from 1925 to 1945, and for five, ten and twenty-day oxygen demand values. The five-day demand is sixty-eight percent of the twenty-day demand and the ten-day demand is ninety percent of the twenty-day value. It is assumed in this computation that the strength of the polluting unit of each polluting element will remain the same during the period of time involved. The second section of Table 19 shows the purification, expressed in percent, required for gross diversions of 2,000, 4,167, 7,500, 8,500 and 10,000 second feet per day and for oxygen demand, values of five, ten and twenty days. The computation showing the percentage of purification required, is simply one of subtraction and division, and may be illustrated by taking the first value in the table viz., 96.4 which is arrived at as follows: ; 19,900 second feet — (2,000 second feet —1,280 second feet) divided by 19,900 or 96.4%. The percentage values in this table are carried to the first place beyond the decimal however, this is not intended to imply that this ; degree of refinement should be followed in the use of these values as they constitute simply a record of a mathematical computation.

With these data in hand and a knowledge of practicable plant efficiencies, it is possible to select the types of treatment works that would produce required results.

Seasonal Variations:

All the computations hereinabove made refer to the critical season of the year, namely, the warm months of July and August. In the winter time each unit of lake water will carry about double the amount of oxygen available during the critical period. Furthermore, oxidation takes place at a slower rate during the cooler months of the year, and the sewage is thus afforded the opportunity to travel further downstream, to be subjected to additional aeration and to be mixed with additional tributary waters.

For all these reasons, it is undoubtedly practicable to regulate the diversion from the lake in accordance Vv^ith the needs of the situation 84 existing from month to month. All the interests affected by diversion of water from the lake are concerned only with an average diversion.

There appears to be no reason why it will not be entirely practicable to materially increase the flows herein estimated for the warm months of the year should occasion arise, and to save the water thus taken during other months of the year, thus staying within a stipulated average diversion.

Factor of Safety:

It must be admitted that it is not practicable to compute exactly the amount of diluting water that necessarily must be added to the sewage in order to obviate nuisance and to permit a thriving fish life. It is desirable that there should be a factor of safety to provide against error.

In our opinion, it will be wise to adopt as the average diversion with various degrees of purification the amounts herein set down as required in the months of July and August, and to use the additional water available in the cooler months of the year as a factor of safety, thus permitting some increase of the dilution in the hot months to cover, (a) The possibility of less reaeration in the lower river than herein contemplated. (b) Washings from the sewers in storm that may be necessarily by-passed from the sewage purification plants. (c) The accidental depletion in the oxygen in the lower river through the sudden death of green plant growths. (d) Some degree of inferiority in the diluting water entering through the Sag Canal and other minor drafts on the oxygen supply not specifically considered herein.

Additional Oxygen: No specific consideration has been given to additional oxygen that may be furnished by the effluent from the sprinkling filter plants and the activated sludge plants. This oxygen will be in addition to that obtained from the lake and from the other sources mentioned.

At the present time practically no aeration is obtained at Lockport in dropping the water from the Drainage Canal into the Des Plaines River in passing through the water wheels. It would probably be possible to add from one to two parts per million to the sewage by an over- fall especially designed for aeration. This possibility will occur at all of the dams hereinafter constructed for navigation purposes on the Illinois River except where the water may be used for power purposes. 85

PART VII. PROTECTION OF THE WATER SUPPLY

It must be a part of any scheme for sewage disposal that the water supply should be protected against any possibility of sewage contamination. Unless this is accomplished sewage disposal fails in its principal requirement.

This matter is particularly important to municipalities located on the shores of the Great Lakes. In all of these cities the lakes constitute the only practicable means for municipal water supply. In many instances the lakes are the only practicable means for sewage discharge. In the Chicago region the means has been provided through the drainage canal, by which the great majority of all impurities are diverted from Lake Michigan. As will be pointed out, certain sources of pollution still remain, and will continue to exist, regardless of any improvements in the Sanitary canal. These sources of pollution are sufficiently great to seriously menace the water supply, unless adequate precautions are taken to guard against them.

Lake Shore Line:

The south end of Lake Michigan is relatively shallow. On the Chi- cago water front the distance outward for twenty-five feet depth varies generally from half a mile to a mile. The four-mile crib at Chicago stands in thirty-six feet of water. The depth of water is five to eight feet less at the other intake cribs, located at lesser distances from shore.

Opposite the mouth of the Chicago River a depth of fifty feet is attained only at seven miles from the shore. Opposite the mouth of the Calumet

River the same depth is only attained nine miles out. Opposite Gary

the lake is deeper ; fifty feet is attained at a distance of four miles from shore.

At the shore line there is a fringe of sand generally varying from ten feet more or less, at Chicago, to about fifty feet in the vicinity of

Gary. This sand is a superficial deposit upon a bed of blue clay. The sand layer generally disappears within a mile or two from shore, and the coating is scattering and thin at this distance out.

Intakes and Pollution Sources:

The accompanying map, Figure 1, shows the Lake Michigan shore line, the location of the Water Works intakes, and the location of the streams forming potential sources of pollution. . :

The distance of the Chicago Water Works' cribs from the mouth of the Chicago River, and Calum.et River respectively are as follows

Miles from Chicago Miles from Calumet River Mouth. River Mouth Wilson Ave. Crib 5.2 16 Carter Harrison Crib 2.3 12.7 Chicago Ave. Crib 1.3 12.2 Four Mile Crib 3 9.3 Hyde Park & E. F. Dunn Cribs 8 3.7

About six miles southeast of the Calumet River mouth, the Indiana

Harbor canal is located, which taps the Grand Calumet River and discharges more or less sewage into the lake. Between these two points lie the Water Works' intakes of Whiting and Hammond, Indiana. The

East Chicago intake is close to the shore, and only a short distance from the Indiana Harbor canal. The Gary intake is one and one-half miles from shore, six miles east of the Indiana Harbor canal and twelve miles from the Calumet River, measured in a direct line.

Sources of Pollution: From the mouth of the Calumet River, north to the Cook County line, the sewers are now diverted from the lake. North of the Cook County line the towns between Highland Park and Waukegan sewer into the lake, except a small population in Highland Park which sewers inland toward the Skokie Marsh. Most of this sewage reaches the lake in a raw state at present. A portion of it is partially purified. These cities are members of the North Shore Sanitary District, intended to prevent excessive pollution of the lake. Conditions in this locality will probably be somewhat improved hereafter.

Indiana Towns:

The Indiana towns from the State line eastward, including Gary, now contain a population of 180,000. These towns are growing very rapidly. They are the sites of some of the largest industries in the

Chicago region. Grand Calumet River is the main sewer of this region. Considerable sewage from the shore population in Hammond and Whit- ing, and from several industries, discharges directly to the lake. The entire City of Gary, and the greater part of the sewage in East Chicago and Hammond drains inland and only reaches the lake through the outlets of the Calumet.

Calumet River:

Attention is invited to the Grand Calumet and Little Calumet Rivers, and their relation to Lake Calumet, the outlet of the two streams into Lake Michigan, and the location of the Calumet Sag Channel. The 87

Sag Channel is now designed for 2,000 second feet. At certain seasons of the year this is sufficient to take the sewage of the Chicago Sanitary

District reaching it and the entire flows of the Grand and Little Calumet

Rivers. In seasons of flood the Sag Channel is very insufficient to take the flow of these streams.

Figure 17 is a watershed map of the Grand Calumet and Little Calumet Rivers. The total drainage area of these streams is 770 square miles. The maximum measured flood in this district occurred in February, 1887. It was measured at Riverdale on the Little Calumet River and amounted to 13,300 second feet. The Sanitary District of Chicago has estimated the maximum flood to be expected from the combined Grand and Little Calumet Rivers at 16,000 second feet. The estimate of the

International Waterways Commission is substantially the same. Continuous gaugings are not available showing the frequency and duration of floods. In a report of Mr. Wisner, Chief Engineer, of the

Chicago Sanitary District, June 9, 1909, it is estimated that with 2,000 second feet flowing in the canal, there would be 22.4 days per year when the flood flow from the Calumet Rivers would exceed the flow of the

Sag canal. The source of the information upon which this estimate is based is not stated. Judging by the experience of the nearest adjoining streams upon which flow records are available, it appears that the above figure may be approximately true. Flow records on the Kalamazoo River, draining somewhat similar territory in Michigan, applied to the Calumet Rivers with drainage area correction, indicate a probabihty of eighteen days per year when the flow of these screams might be expected to exceed 2,000 second feet. A similar comparison based on daily gaugings on the Des Plaines River, corrected for drainage area, indicate about twenty-five days flow in excess of 2,000 second feet. A large flood on these streams will undoubtedly wash great quantities of filth into Lake Michigan. The Calumet cities are beginning to study the question of sewage purification. Conditions in the future will no doubt be improved. No practicable means for sewage purification will place these streams in condition where their waters may be period- ically flushed into the water supply of the region even occasionally, with safety to the water supplies.

Water Level Changes: The lower Calumet River, between Calumet Lake and Lake Michi- gan, is dredged 200 feet wide and twenty-one feet deep. It requires a slope of only a small fraction of an inch from Lake Calumet to Lake Michigan to discharge 1,000 second feet. A difference in level of slightly over two inches will discharge 5,000 second feet. A recording guage at 88 ;

89 the mouth of the Cahimet River shows that the surface of the lake is constantly rising and falling, due principally to changes in direction and velocity of the wind. Changes of six inches in less than an hour are very common. It is an exceptional day in which the total variation is less than six inches at different times during the day. Upon moderately windy days the variation is frequently more than one foot. Some years ago we conducted a systematic watch of the currents in the lower Calumet River, estimating the current velocities by rod floats This study confirmed what would be expected by the water level variations in Lake Michigan, and the comparatively large volume of stagnant water in the Calumet Rivers and Lake Calumet. Whenever the lake surface dropped a few inches a rapid current was set up toward Lake Michigan, which continued until a change in the wind caused the lake surface to rise, in which case if the rise was great enough the outflow was stopped, the current reversed, and often a rapid current ran inland for several hours, to return again with a subsequent fall in the lake level. Thus on February 20, 1920, with a variation in lake level of about three tenths of a foot and a brisk northwest wind gradually decreasing after

3 p. m., the flow of the river varied from 1,000 second feet from the lake at 2 p. m. to 3,000 second feet toward the lake at 5 p. m.

On February 11th, with a brisk northeast wind, the flow from 1 - to 5 p. m. varied from 1,000 to 1,500 second feet landward. For short periods it became nearly stagnant. On February 12th with a mild southwest wind the flow averaged about 2,000 second feet toward Lake

Michigan from 1 to 3 p. m., but stopped entirely as the wind died down about 4 p. m. Thus the Calumet Rivers and Lake are constantly ''breathing" in and out, toward and from Lake Michigan, depending principally upon the direction and velocity of the winds. In severe storms there are also very important barometric changes causing lake level fluctuations of several feet, bringing out heavy discharges for periods of many hours. No doubt a similar condition exists where the Indiana Harbor canal taps the Grand Calumet River. This is a wide and deep harbor only a small difference in head, an inch or less, is required for the inter- change of water between the river and Lake Michigan. The sewage of Gary is supplemented by a large amount of condensing water from the steel mills. A rapid flow is produced in the upper Grand Calumet. The final disposition of this sewage laden water depends upon the stream cross-sections, and the relative elevations of the moment as between the Calumet Rivers and Lake Michigan. 90

Chance Pollution from Chicago River: Prior to the construction of the drainage canal, conditions at the mouth of the Chicago River were somewhat similar to those previously described as prevailing" in the Calumet region. The floods of the Chi- cago River have not been accurately measured. It has been estimated that the discharge capacity of the storm water sewers in Chicago makes

it possible to produce a flood of about 11,000 second feet. Possibly it

may be questioned whether this is so at the present time. If it is not

true today it probably will be true as the city becomes improved to a greater extent than at present. With the drainage canal in operation at the rates of flow, which have prevailed during the past ten years, there is little danger of a material amount of flood water reaching Lake Michi- gan. There have been a few occasions, however, for a short time when a lakeward flow has been noticed following great rain storms. With lesser flows in the drainage canal these occasions would become more frequent and of longer duration.

At the present time lakeward flows of water would be very detrimental to the Chicago water supply. With the general adoption of sewage purification works, and the consequent cleaning up of the Chi- cago River, the dangers resulting from a lakeward flow of water would

be diminished but there would still be a potential danger to the water supply. The purification of the sewage would not be a determining fac-

tor in the matter further than to diminish the quantity of filth that might be washed into the lake by flow reversal.

Travel of Pollution in the Lake: _ The question as to the travel of pollution in the waters of Lake Michigan has been studied very thoroughly upon several occasions covering the Chicago water front, the water front opposite the Chicago north shore suburban towns aixl further north along the lake at Racine and Milwaukee. The results of these studies indicate similar conditions wherever sewage contamination reaches the lake and variable winds and waves are available for dispersion. The net results from these studies are well summed up by Major W. V. Judson in his paper on currents in Lake Michigan, (first report Lake Michigan Water Commission, page 67).

"In my opinion the currents of Lake Michigan are so irregular in character that nothing would be gained worth the cost if attempt were made to obtain classified further data of a general nature. If it is a question of pro- tecting the water supply of any particular locality, in any event, special study would have to be made inasmuch as the lake currents, available as they are, are much influenced by local conditions. 91

We do know, and perhaps it is enough for the purposes of this commission, that occasional currents of considerable velocity, say several miles per hour, may be expected to arrive from almost any direction at any point reasonably near either shore of the lake. It is, therefore, apparent that in a general case if the waters of the lake are polluted by the discharge into it of large quantities of sewage, then, practical localities in the lake, even twenty or thirty miles distant from the point of entrance to the sewage, are not safe places in which to derive water for domestic use."

Numerous special investigations of lake water condition, and the practical experience in the operation of the water works intakes, all indicate that in any particular place reasonably adjacent to the lake shore the quality of the water varies between extremely wide limits, including water almost sterile for considerable periods of time, the usual prevalence of moderately heavy pollution, depending upon the locality, with occasional gross pollutions, regardless of locality within practicable reach of a water works inlet.

Turbidity:

In drawing a continuous supply for the wrater works, it is necessary to locate the intake not closer than two or three thousand feet from the shore, in order to prevent ingress of sand and stoppages from anchor ice. A large supply must necessarily be taken further from the shore. The Chicago intakes are located from two to four miles outward. Upon the west shore of Lake Michigan there are long periods of the summer season when the prevaihng winds are from the west and southwest. At such times the surface water is blown out into the lake and is replaced by a return current along the lake bottom. At such times as this an exceptionally clear and pure water may be drawn from an intake located at or below mid depth, in twenty-five to forty feet depth. Severe storms usually occur with an east or northeast wind, The surface water is blown in toward the shore, breakers are formed in the shallow water, the dirty sand and accumulated sludge adjoining the shore are stirred up and the water is returned lakeward as an undertow.

The filth is, however, more or less intermixed, from bottom to top of water, in depths under fifty feet. At such times as this no clean or pure water can be obtained ; the degree of the turbidity and extent of pollution depends principally upon the severity of the storm and somewhat upon its direction. Wind conditions varying between the two extremes, which have been mentioned above, produce water conditions varying between the extremes of quality previously mentioned. There are certain conditions in storms when pollution may travel with great rapidity to a Water 92

Works intake. The situation is much like the dissipation of smoke from a tall chimney. In relatively calm weather it may disappear within a short distance from the chimney. Under a current of wind it may stream out in one direction, traveling for miles. Pollution in a lake may travel in similar manner.

Present Condition of the Water Supply: About two-thirds of the time the water drawn from the Chicago cribs is clear. It is often quite pure for short periods. However, its sanitary character cannot be depended upon from hour to hour. For a considerable portion of time at all the intake cribs it is distinctly bad. It can only be safely used after heavy doses of liquid chlorine. The required dosage has increased of recent years. Occasionally the Health Department has advocated boiling. The water as delivered to consumers is often decidely turbid for weeks at a time. The net result from a sanitary standpoint from the water as chlorinated has been very good, although there have been times when it has been suspected of producing typhoid fever in local instances, apparently due to chance pollution. To a large number of people the taste imparted to the water through the chlorine dosage is extremely objectionable.

The demand is becoming stronger from year to year for a water free from the chlorine taste.

Records of Turbidity: The two mile crib supplying the Chicago Avenue pumping station and a part of the water of the 22nd St. Station furnishes about one-fifth of the total water supply of the city, including the downtown district. Table 20 shows the prevailing turbidity of the water drawn from this crib during the past ten years. In the consideration of turbidity, which represents the apparent cleanliness of the water, it should be stated that a clean water, such as produced by water filtration plants, has a turbidity of about five. A turbidity of ten is noticeable by people accustomed to clear water. A turbidity of fifteen would cause serious complaint where people are accustomed to clear water. A turbidity of fifty represents a very dirty water that would desirably be treated by sedimentation before application to a mechanical filter. The records for the two mile crib shows that the water has a turbidity more than ten practically at all times. It has a turbidity above fifty for periods totaling from two to seven weeks per year, excepting one year. This crib being the nearest to shore generally has the highest turbidity as compared to other Chicago cribs. 93 ooooooooo 01

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Table 21 shows the maximum and average*turbidities at each of the

ChicagT cribs. The average turbidity was less than ten a little more than haii the time during the year 1924, up to October. The average turbidity at all the cribs ranged between twenty and thirty-five during February, thirteen to twenty-five during March, and ten to fifteen during April. The maximum turbidity was above ten at most of the cribs during the months of February to October inclusive. It was above fifty at all the cribs during February, from 30 to 55 during March, from eighteen to fifty during April, and ten to forty in May.

Filtration:

All objection to the piesent water supply can be eliminated by mechanical filtration, which it is practical to apply to the Chicago watc; supply at a comparatively moderate expense. Filtration will give the citizens of Chicago pure clean water all the time, eliminating all possibility of danger from the chance pollutions of the lake. A number of cities upon the Great Lakes have already installed filtration works, including several of the srnaller cities in the Chicago region, also including the cities of Detroit, Cleveland, Lorain, Erie and Niagara Falls. In several cases highly polluted waters are rendered entirely satisfactory for domestic consumption.

Polluted Waters Treated:

At several places, on the Great Lakes, lake water is safely filtered after receiving the sewage of the city supplied through intakes removed only a comparatively short distance from the sewage outlets. Cleveland is an example of this type. At Cleveland the water is taken within 19,000 feet from sewer inlets receiving only partially purified sewage. Upon the Ohio River, city after city, from Pittsburgh to Cairo, takes its water supply from the river, returning the sewage again to the stream, the water being again and again used by the cities downstream after filtration. Table 22 shows a list of these cities with approximate distances measured by river, from sewage outlet to water works intake.

Although it has been felt desirable, and is proper in all cases in the water supply of cities, to select ^mre a source as possible even when filtration is resorted to, it has been necessary in some cases to filter more or less grossly polluted water. The results from the sanitary standpoint can safely be said to have exceeded expectations wherever filtration has been resorted to. 97

TABLE 22. SUCCESSIVE POLLUTION AND USE FOR WATER SUPPLY OF THE OHIO RIVER FROM PITTSBURGH TO CAIRO.

City Using Filtered River Water Nearest Principal Source of Pollution Miles Miles Popu- Below Popu- Up- lation Pitts- lation stream City 1920 burgh City 1920 Pittsburgh 588.343 ! Beaver ) 50 E. Liverpool 21,411 ''''' Monaca [ 66 Toronto 4,684 20 Wellsville 8,849 80 Steubenville 28,508 8 Toronto 4,864 105 Wheeling 56,208 25 Steubenville 28,508 110 Bellaire 15,061 5 Wheeling 56,208 190 Marietta 15,140 73 Moundsville 10,669 202 Parkersburg 20,050 12 Marietta 15,140 322 Huntington 50,177 37 Gallipolis 6,070 340 Ashland 14,729 4 Catlettsburg 4,183 344 Ironton 14,007 4 Ashland 14,729 372 Portsmouth, 33,011 28 Ironton 14,007 498 Cincinnati 401,247 126 Portsmouth 33,011 499 Newport 29,317 126 Portsmouth 33,011 520 Aurora 4,299 22 Cincinnati 594,000* 534 Louisville 234,891 136 Cincinnati 594,000* 539 New Albany 22,992 5 Jeffersonville 10,098 B04 Evansville 85,264 35 Owensboro 17,424 ^15 Henderson 12,169 11 Evansville 85,264 ?37 Mt. Vernon 5,284 25 Henderson 12,169 105 Henderson 12,169 934 Paducah 24,735 130 Evansville 85,264 979 Cairo 15,203 45 Paducah 24,735

*Including adjoining river towns.

Niagara Falls:

A typical example as to whd.t filtration can accomplish with a freshly polluted water is instanced by the experience at Niagara Falls, New York. For many years prior to 1913 this city was one of the most important typhoid centers in the U !:tcd States. The city water supply is taken from Niagara River a few hours after the water receives the sewage from more than 500,000 people at Buffalo, and from other smaller cities downstream. The accompanying Table 23 shows the typhoid history of Niagara Falls prior to and following the installation of filter plants in the year 1913. Two plants were installed. The municipal plant went into service in February and the New York Water Company's plant went into service in June, 1913. For a period of eigh- 98 teen months shortly following the installation of the filters no typhoid deaths occurred in the city, although shortly prior thereto and for many years previous the typhoid death rate had commonly exceeded 100 per hundred thousand per annum. Within the past ten (10) years there have been only a few cases reported, a careful tally of them has been kept, and it is stated they have not been traced to water supply.

Cost of Filtration for Chicago:

It is believed that the most feasible plan for filtering the Chicago water supply will consist of plants located on the lines of the intake channels at or close to the Lake Shore line. The city could be served by four (4) plants, namely at Wilson Avenue, Chicago Avenue, Roosevelt Road and 67th St. It would be practicable to install bulkheads and

TABLE 23.

TYPHOID DEATH RATE AT CITY OF NIAGARA FALLS, N. Y. Typhoid Typhoid Estimated Death Rate Year Deaths Population per 100,000 Remarks 1899 24 17,261 139 1900 24 19,457* 123 1901 29 20,362 143 1902 22 21,267 103 1903 29 22,172 131 1904 34 25,037 135 1905 49 26,432 185 1906 43 27,827 154 1907 37 28,000 132 1908 28 29,000 97 1909 24 29,793 80 1910 32 30,445* 105 1911 55 32,800 168 1912 23 35,000 66 1913 10 37,000 27 BeganB( water filtration** 1914 3 39,000 7.7 1915 41,000 1916 5 43,000 11.6 1917 5 44,800 11.1 1918 2 46,600 4.3 1919 2 48,500 4.1 1920 5 50,760* 9.8 1921 5 52,600 9.5 1922 2 54,800 3.6 1923 1 57,000 1.8 1924 3 59,000 5.1

*U. S. Census. **Municipal Water Filtration Plant put in operation in February. **Westem New York Co. Filtration Plant put in operation in June. :

99 gates in the tunnels, pump the water to the surface, pass it through sedimentation basins and filters, store it in clear water reservoirs of moderate size, and return the water again to the tunnel system beyond the shore gates where it could pass as at present to the pumping stations.

It is stated that the water in the tunnel system now receives some pollution from unknown sources after entering the tunnels. The City

Engineer states that his investigations indicate that this pollution is probably confined to pollution at certain shafts. It seems hardly possible that pollution could enter the tunnels proper, after passing landward from the shore line. It is feasible to stop the surface pollution at the shafts, if it exists. It is further possible in the design of the filter w^orks to eliminate any possibility of pollution by adopting an hydraulic grade line in the tunnel system above the ground water plane. This would be possible by extending the shafts at the pumping stations to a higher elevation and pumping water to a corresponding height at the shore line. This could be done without increased cost of pumping. It is practicable to purchase low lift pumps in large units that will have an efficiency substantially equal to the pumps used in delivering water to the city, and there would be no net loss of head. In several instances the filtration plants could be located in existing city parks, or in connection with the lake shore park improvements now under way. It is possible to design the plants so that they would add materially to the beauty and interest of the parks. Where the lake shore is not proposed to be used for park purposes, it is possible to construct the plants upon made ground closely adjoining the shore line. Much ground of this character has already been made adjacent to the city, and is in process of making in connection with Chicago's lake front improvements. Tentative estimates made by City Engineer, John Ericson, on the filtration of Chicago water are as follows

Total annual in- Q.^jg Annual expense perudy* Investment Operating eluding 5% in- Expenses terest and 2% depreciation

Wilson Ave. Plant 200 $ 4,000,000 $ 234,335 $ 514,335 Chicago Ave. Plant 500 10,000,000 676,705 1,376,705 Roosevelt Rd. Plant 155 3,100,000 188,120 405,120 eSth St. Plant 445 8,900,000 651,000 1,274,000

Totals 1,300 $26,000,000 $ 1,750,160 $ 3,570,160

The above estimate covers an installation that would be sufficient to filter the present water supply. If the water supply of the city is metered, the above plant would serve all requirements of the city until 100 after the year 1960, making due allowance for the seasonal and hourly variations in pumping.

The above total cost is approximately $8.65 per capita on the present population of Chicago. The average annual cost, including operating and fixed charges, is approximately $1.20 per capita on the present population, and would be materially less under the increased population of Chicago during the next thirty years during which the investment would be effective.

Conclusion Regarding Filtration:

Chicago is entitled to a clean water, safe from a Sanitary standpoint 365 days per year. This standard is generally demanded throughout the United States. It is only a question of time when it will be demanded in Chicago. In our opinion filtration will insure a pure clean water for Chicago at all times, under any diversion through the drainage canal exceeding

2,000 second feet. It is our belief that no amount of diversion up to the present capacity of the Chicago drainage canal will insure safe water for Chicago without filtration. We believe this is true regardless of any practicable measures that may be taken for sewage purification.

We believe it is the only adequate safeguard for the Chicago water supply. 101

PART VIII. SAVINGS EFFECTED BY METERING.

The quantity of municipal sewage is largely dependent upon the water supply. In Chicago where the population for which sewage treatment is to be provided is large, the industrial load is great, and the amount of water pumped is extravagant, the problem of keeping expenditures for sewage treatment works reasonably low, is difficult. The first two factors, i. e., population and industrial wastes, are fixed as of

any particular time ; the last factor, water pumpage, is capable of regu- lation. The question of water waste restriction is acordingly a sewage disposal problem as well as a water supply problem. With this in mind a study of the effect of metering on the costs of sewers and sewage disposal has been made herein and incidental thereto certain observations as to the effect upon the water works and water service are included. At the present time ninety percent of all of the consumers furnished water by the Chicago Water Works are served through socalled ''flat rates" under which there is no incentive to keep plumbing in repair, nor to curtail other wastes. As a result the pumpage of water is excessive, the water service is deficient as to quantity, qualify and pressures, and the Water Department is confronted with the continual necessity of making large expenditures in its hopeless effort to keep pace with the open faucet. In 1923, the last year for which published records are available, but

9.65 percent of all services were metered. The water passed through these meters was 30.4 percent of the total pumpage. The revenue de- rived from the sale of metered water was 57.96 percent of the total revenue of the Water Works. The metered water consumers paid an average of approximately six and one-fourth cents per thousand gallons for the water consumed.

Approximately seventy percent of the gross pumpage which is unmetered yielded a revenue equivalent to approximately two cents per 1,000 gallons, or less than the actual cost of pumping.

Water waste is directly reflected in the costs of construction, and the cost of operating the Water Works plant. In the past thirty years, during which the population and the mileage of mains have increased approximately 150 percent, the cost of im.provements to the Water Works and the average daily pumpage have increased approximately 102

400 percent, or at a rate two and a half times as fast as the population. Pumpage and construction costs increase at approximately parallel rates. Water waste results in deficient water pressures throughout the greater part of the city. At the present time approximately seventy-five percent of the area of the city of Chicago suffers from inadequate pressure during periods of peak consumption. Water waste decreases the effectiveness of fire protection service.

Water waste is directly reflected in the dry weather sewage flow. It therefore increases the costs of constructing intercepting sewers, sewage pumping stations and sewage disposal plants ; it is also directly reflected in the operating costs of sewage pumping stations and sewage disposal plants.

Curtailment of Waste:

Ample precedent and experience are available from which it is practicable to determine, within reasonable limits of accuracy, the possibilities of waste restriction for Chicago, and its effect upon costs of water service and sewage disposal. Table 24 presents the data relative to results accomplished by metering in eleven American cities. Figure 18 shows diasframmatically what has been accomplished by meters in these and other cities. Numerous studies have been made of the particular problem of restricting waste of water in this city. All in-

TABLE 24. EFFECT OF METERING UPON THE CONSUMPTION OF WATER.

Use of Water in Gallons per Service Before After Extensive Extensive City Metering Metering 1048 396 1108 734 Cleveland, 1258 688 Milwaukee, Wis 1314 656 Lowell, Mass 630 427 838 396 853 383 2240 1165 1560 508 1035 635 755 599

1149 599 6.7 95.0 Average reduction by increasing meters from 6.7% to 95.0% was from 1149 to 599 gallons per service or 48%. 103 vestigators have been in substantial accord as to the immense savings in cost and benefits in service which would result therefrom.

Quite recently, at the mid-winter convocation of the Western Society of Engineers, held in February, 1925, Mr. John Ericson, for nearly thirty years city engineer of Chicago, presented a paper on 'THE WATER SUPPLY PROBLEM IN RELATION TO THE FUTURE CHICAGO." In this paper Mr. Ericson effectively showed -

104

the need of metering and the results which might be accompHshed there-

Mr. Ericson estimated the pumpage requirements which the Chica- go water supply would be called upon to meet if the present system of metering were to continue, and also what these requirements would be

if all water consumers were to be metered within the next ten-year period.

The results of this analysis are shown in diagrammatic form on

Figure 19. It is estimated that the total pumpage in 1924, of approximately 800,000,000 gallons per day will increase to 2,200,000,000 gallons

per day by 1960, if the present system of metering is continued. If,

however, all water servtces are metered within the next ten years the total pumpage of approximately 800,000,000 gallons per day at the present can be reduced to approximately 520,000,000 gallons per day in 1935, increasing to 800,000,000 gallons per day by 1960. In other words, the pumpage with universal metering, thirty-five years hence will be less than the pumpage at the present time with but ten percent of the services metered. We have carefully investigated this matter and we believe that Mr. Ericson's estimates of reduced pumpage are approximately correct.

This fact has an important bearing upon water works construction costs. No additional crib intake or pumping station capacity and no expenditures for feeder mains would be required for the next thirty-five

years if universal metering were to be adopted.

The savings to the Chicago Water Works, due to metering, have been estimated at from $225,000,000 to $425,000,000 in the next twenty- five to thirty-five years. Mr. Ericson, based upon a population of 5,000,000 people in 1960, figures that the saving in operation up to that time will be $117,000,000, the saving in repairs and renewals $43,000,000, and the saving in additions and extensions $143,000,000. Total saving $303,000,000. This saving does not take into consideration

fixed charges on the savings in new construction, which if taken at a rate of five percent and based upon the construction expenditures being made at a uniform rate from the present time to 1960, would add an additional $125,000,000, making the total saving to the Chicago Water Works amount to $428,000,000 by 1960. In a paper "What metering would do for the Chicago Water Works" presented before the Western Society of Engineers by L. R.

Howson on February 1, 1923, it was estimated that the savings prior to 1950, due to universal metering would be $88,000,000 in construction expenditures, $145,000,000 in operation, including saving in fixed « —

105

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From paper by John Ericson read before Western Society of Engineers. charges, total saving $233,000,000, or approximately eight and one-half million dollars per year.

Other estimates have been made, all of which show the enormous savings which can be effected by metering. The exact amount is not of so much importance when the lowest estimates that have been made by competent engineers investigating this matter show a saving in the next generation of over $200,000,000.

Effect of Metering on Intercepting Sewers and Sewage Disposal Costs:

The amount of water reaching the sewers is important in the design of intercepters and sewage disposal works. The costs of a large part of this type of construction are directly proportional to the quantity of sewage to be treated. 106

Intercepting Sezvers:

The capacity of intercepters is directly affected by the amount of

the water supply, practically all of which reaches the sewers. If the

water pumpage is excessive and can be reduced to the extent of thirty- five percent the intercepting sewer sizes can be reduced about twenty percent and the cost a somewhat smaller percentage. In view of the large mileage of intercepting sewers yet to be built the question of the

water supply and its eft'ect upon intercepter sizes is important. At the present time the intercepting sewers for the Des Plaines and Calumet plants have been completed. The intercepters leading to the

North Side plant are all under contract, and construction is well on toward completion. The intercepting sewers leading to the West and Southwest plants have not yet been started. Intercepting sewers for the West Side plant, as tentatively designed by the Sanitary District, include an approximate length of twenty miles of large size, the maximum being twenty-one and one-half feet in diameter. The tentative design of the intercepting sewers for the Southwest plant includes some fifteen miles of sewers, varying in size from five to eighteen feet. In view of the status of the intercepting sewers for these two plants yet to be built, it is pertinent to inquire into the affect of metering upon the design and costs of these sewers. We have been furnished by the Sanitary District with the basis of design for the West and Southwest sewers. They have furnished us with the drainage areas tributary at points of interception, the population estimated as being located on each drainage area in 1960, the industrial use as estimated by the Sanitary District in cooperation with the City Water Department, and figures as to infiltration. The total sewer capacity average over the entire district amounts to 600 gallons per capita per day.

Based upon figures as furnished by the Sanitary District, the tentative design made by the District's engineers contemplates that the sewers will flow three-fourths full under peak flow conditions. How- ever, under the use of water estimated by Mr, Ericson and others under present conditions of metering, the sewers would be flowing full instead of three- fourths full if universal metering is not adopted. The average use of water if unmetered will be 440 gallons per capita per day.

If thirty-five additional is added for the peak flow excess over average the entire sewer capacity is required. With the entire water supply metered the average use of water would be but 160 gallons per capita per day or 280 gallons per capita per day less than if the present system is continued. Deducting this amount from the capacity allowed in the Sanitary District's estimates 107 an equivalent capacity of 320 G. P. D. per capita would be indicated.

This is a lower figure than we would however care to adopt and we have arbitrarily raised it to 375 gallons per capita per day. The effect of metering upon sewer costs is therefore made on this basis. The sizes of sewers required under both the metered and unmetered bases have been determined for each reach of the intercepters serving the West and Southwest areas in which construction for sewage disposal has not already started. Comparable grades and velocities were assumed. The costs of the intercepters were estimated using the unit prices developed as described in Part X. It was found that metering will effect a saving of $3,105,500 in the cost of the intercepters to the West Side plant, and $2,043,800 in the cost of the intercepters to the South- west Side plant; a total of $5,149,300. This saving results from metering alone. It is a saving perfectly practicable of realization. Metering must eventually come. Had the actual costs of sewers built under contracts let by the Chicago Sanitary District been used as a basis of the comparison the indicated savings would have been much greater. Metering cannot be retroactive in saving expenditures on sewers

built ; it will however, greatly extend the period of adequacy already , of such sewers. In view of the ultimate necessity for metering the Chicago Water

Supply, as agreed by all engineers who have given it thorough study, it would seem a wise procedure to give due consideration to this question in the design of sewers by the Sanitary District. Sewers built for the present without meters will be adequate for 1960 with meters.

Effect of Metering on Sezvage Disposal Plant Costs: The cost of certain parts of sewage disposal plants varies directly with the quantity of sewage to be handled. These parts include pumping stations, grit chambers, screens and aeration tanks ; other parts vary directly with the solid or organic load of the sewage. These parts include sludge chambers of Imhoff tanks, sludge beds, and sludge pressing and drying equipment, for activated sludge plants.

Other parts of the plants vary in a ratio which is neither directly in proportion to organic load nor to the quantity coming to the plant. This refers particularly to air compressor equipment and to sprinkling filters. It has been found practicable to load sprinkling filters handling domestic sewage with 2,000 to 4,000 people per acre foot depth of sprinkling filters. It has also been found practicable to put sewage through these filters at rates as high as 2,500,000 to 3,000,000 gallons per acre per day without operating difficulties. 108

The following table shows the operating rates on several plants operating satisfactorily under reasonably heavy loadings.

Sprinkling Filter Loads.

Pop. Acre Fact of Pop. City per Sewage per Served Stone Filters Acre foot capita (gal.)

AAA 1 OA Lincoln, Neb . . 50,000 + D X ^.o -Id. 5 O,UU0 + 80

Madison, Wis . . 51,500 6X2.5:=15 (a)3400 (a)102

Columbus, . .270,000(1920) 51/3X10=:53.3 5060 100 Atlanta, Ga,

Intrenchment , 30,000 5%X2=:11.5 2730 167

Lexington, Ky . 28,000 6X2:=12 2330 90

Baltimore, Md , ,600,000(1924) 8y2X30==255 (a)2360 86 As operated for best results (a)3500 Average 3200 104

(a) Excliisive of packing house waste.

At Baltimore where there is a total of thirty acres of stone beds the units are operated so as to maintain as nearly as possible from two

and one-half to three million gallons per acre per day rate (average is from 2.79 to 2.91, C. E. Keefer, Engineering News Record, 2-7-24), the equivalent under Balitmore conditions of approximately 3500 people per acre foot of stone beds. Included in this optimum loading of 3500 people per acre foot of

stone filters is a packing house waste, which, based upon weight of ani-

mals slaughtered per capita contributing sewage to the plant, is about thirty-five percent as great as that of the Chicago stockyards wastes.

The Madison stone filters, aperating satisfactorily at a rate of 3400 people per acre foot have in addition a packing house waste practically the same as the Chicago stockyards waste, compared on a slaughter weight per capita basis.

A study of the effectiveness of sprinkling filters in reducing the biochemical oxygen demand shows that the Baltimore and Columbus filters reduce the demand sixty-seven and fifty-five percent respectively as compared to thirty-one, thirty-one and forty-nine percent respectively for the two Atlanta and Fitchburg plants with population loads per acre foot, but about half of those at Baltimore and Columbus.

It is our opinion that good operation may be secured within the upper limits of at least 3,000 people per acre foot, and three million gallons per acre per day for six foot stone beds. As with a per capita use of 160 gallons per day the population served by a six and one-half foot filter operating at a three M. G. D. per acre rate would be about 2850 per acre foot the rate of liquid dosage :

109 rather than the population load is considered the limiting factor in com- paring the cost of sprinkling filters at Chicago under metered and unmetered conditions. In the estimated savings on the item of sprinkling filters, ef¥ected by metering, we have therefore assumed that the more dilute sewage, tinder unmetered conditions, would have a direct effect on area and cost of beds. In other words, if the quantity of sewage is doubled due to water waste the area and cost of stone beds would likewise be doubled compared to areas and costs under fully metered conditions.

The effect of metering upon plants already built is to prolong their period of usefulness and defer the time at which additions will be required. Each plant has been analyzed in its component parts, its capacities studied with reference to future needs under metered and unmetered water supply conditions, and the savings effected by universal metering ascertained.

The following is a summarization of the savings which universal metering will effect in the future construction costs of intercepters and sewage disposal works.

Savings in intercepter costs are computed for 1960 quantities ; disposal plants for 1945 conditions. The total savings of approximately $50,000,000 do not include any savings in the construction cost of sewage disposal works to the Chicago Sanitary District after 1945. The savings cover the cost of construction only, operating cost not having been taken into consideration in this part of the study.

The small estimated saving with a flow of 4167 c. f. s. results from the fact that a larger part of the cost of an activated sludge plant is independent of liquid volume than is the case with a sprinkling filter plant. The sludge drying and pressing equipment varies only with the solid content which is in turn independent of the dilution of the sewage.

The 4167 c. f. s. project is the only one contemplating activated sludge treatment at the West and Southwest Side plants.

Savings in Operating Costs:

The restriction of water waste will also have a marked effect upon operating costs of pumping stations and disposal works. Practically all the costs of sewage treatment in plants such as herein considered vary nearly in proportion to Hquid quantities, except costs incident to sludge handling and sludge drying, which are practically independent of liquid volume. In estimating the savings in operating cost due to metering, the following bases have been assumed (a) The cost of power varies directly with the liquid volume. (h) Pumping station labor costs vary at a rate of fifty percent as '

110

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great as the variation in liquid volume, i. e. if the liquid volume is doubled the station labor is increased fifty percent. (c) Labor for sewage treatment plant operation varies as above for station labor as the costs are approximately fifty percent determined by liquid volume and fifty percent by total solids or sludge. The estimated savings in disposal plant operating expenses resulting from metering of the water supply have been estimated as above outlined for the year 1945. The savings vary from $3,000,000 to $4,000,000 per year depending upon the treatment processes necessary with the flows in the channel varying from 10,000 c. f. s. to 4167 c. f. s.

TABLE 26.

SAVINGS IN OPERATING COSTS (1945) OF SEWAGE DISPOSAL WORKS (EXCLUSIVE OF FIXED CHARGES) — EFFECTED BY METERING THE WATER SUPPLY.

Cubic Feet per Second Flow in Channel. Plant 4167 6000 7500 8500 10000

Calumet $ 174,750 $ 174,750 $ 174,750 $ 174,750 $ 174,750 North Side 947,000 947,000 947,000 947,000 947,000 West Side 1,869,500 1,288,500 1,288,500 968,000 968,000 Southwest Side 1,289,500 850,800 636,800 850,800 850,800

Total Annual $4,230,750 $3,261,050 $3,047,050 $2,940,550 $2,940,550 Basis. Sta. labor varies 50% with liquid volume—50% not affected by volume. Power varies directly with liquid volume. Treatment plant operating cost varies 50% with liquid volume and 50% with solids.

These savings in operating cost do not include savings in fixed charges which at four percent for interest and two percent for depreciation reserve would amount to from $2,500,000 to $3,000,000 per year in 1945. The estimated saving in operating cost resulting from metering for each flow is shown in the table included herewith.

Summarisation of Savings by Metering: A study of the estimated savings to the Chicago Water Department during the thirty-five year period to 1960 and other estimated savings for other periods would lead us to believe that not less than $200,000,000 to $225,000,000 would represent a fair measure of the total savings

(including interest) to the Chicago Water Works prior to 1945 if meters were adopted and universally installed within ten years. Add 112 to this $200,000,000 saving in the water works, an additional saving of $40,000,000 to $53,000,000 in sewers and sewage disposal and the amount becomes $240,000,000 to $253,000,000 saved in twenty years, an average of over $12,500,000 per year, through the introduction of universal metering, and without crediting any savings after 1945. An additional amount reaching $3,000,000 to $4,000,000 per year in 1945 will be saved in operating costs of pumping stations and treatment works.

Magnitude of Savings: The estimated saving of approximately $250,000,000 in twenty years is so great that it will in addition to installing meters at a cost of approximately $10,000,000 build complete filtration works for the Chicago water supply at an estimated cost of $26,000,000 (Mr. Ericson's W. S. E. paper) finance complete sewage disposal for the entire city and still leave over $100,000,000 net, which would be more than enough to acquire the elevated lines and make a good start toward the subway system.

Effect of Metering on Water Sermce:

In addition to the financial advantages, metering alone will double the average pressure in the water m.ains of the city, and will enable the water works to furnish all consumers adequate service, where but twenty-five percent now have it.

Water metering will make filtration possible. Without it Chicago must continue to drink unfiltered and at times turbid lake water, highly chlorinated with resulting tastes and odors.

Eifect of Metering Upon Protection of Health: Few sanitary engineers will dispute the assertion that $36,000,000 spent for meters and filtration plants will do more to protect the people of Chicago from water-borne disease than will an equal or larger amount spent for sewage disposal works.

It has been estimated that with a diversion of but 4167 c. f. s. there would be from seven to eight reversals of flow with discharge of sewage into the lake each year (see memorandum concerning drainage and sewage conditions at Chicago, Sanitary District, December, 1923). It is believed to be a safe assertion that seven or eight reversals with filtration would be much less hazardous than the one to four reversals now occurring.

Filtration is the first line of defense against water borne disease. Its results are positive, continuous and effectual. It has repeatedly demonstrated its ability to safeguard the public health. 113

Filtration is only practicable at Chicago if universal metering is adopted. Its cost, together with large additional savings, can be re- covered by metering. Metering is, therefore urgent to : (a) Protect health against water borne disease. (b) Enable the water plant to furnish adequate service and pressure (c) Prevent wasteful expenditures for the waterworks. (d) Prevent wasteful expenditures for intercepting sewers and se\vage disposal works. :

114

PART IX. VOLUME OF SEWAGE.

The volume of sewage liquid to be treated is dependent upon

1st. Tributary population. 2nd. The total water use, and 3rd. Infiltration. So far as the sewage contributed by the domestic population of the

Chicago Sanitary District is concerned, practically the entire amount will be collected in the five major sewage disposal plants; viz. The Des Plaines, Calumet, North Side, West Side and Southwest side. The distribution of the population for the present and for each five year period up to 1945, is shown on Table 27. It will be noted that the total population tributary to these five major plants is somewhat less than the total population of the district as estimated in Part III, and as shown in this table. It is estimated that approximately 105,000 people residing in the district are not tributary to any one of these five plants at the present time, and that it is probable, due to the rapid expansion of the suburban area, that this number will gradually increase and reach approximately 300,000 people by 1945. The sewage originating from this population must either be treated by outlying plants or by pumping to one of the major plants.

TABLE 27. POPULATION TRIBUTARY TO EACH OF THE FIVE MAJOR SEWAGE DISPOSAL PLANTS.

Disposal Plant 1925 1930 1935 1940 1945

Des Plaines . . 50,000 60,000 75,000 90,000 105,000 Popula- Calumet 190,000 225,000 255,000 290,000 320,000 tion, by N. Side 690,000 800,000 915,000 1,015,000 1,125,000 Sanitary W. Side* . .1,370,000 1,430,000 1,490,000 1,550,000 1,615,000 District I .• 1,040,000 1,135,000 1,230,000 1,322,000 I S. W. Side. 950,000

Total 5 Major Plants 3,250,000 3,555,000 3,870,000 4,175,000 4,487,000 Misc. Plants 105,000 155,000 200,000 250,000 298,000

Total Population of Dist. .3,355,000 3,710,000 4,070,000 4,425,000 4,785,000

*Excl. of 300,000 transient loop population. 115

The table showing the distribution of the total population of the district over the five plants leaves out of consideration the floating or transient population, largely centered over the area tributary to the West Side plant, which embraces the loop district. This floating population is estimated at 300,000 people, both for the present and for 1945, and in the quantities of sewage which are estimated as reaching the West side plant, the resident population has arbitrarily been increased 300,000 people to care for the transient population.

This figure of 300,000 is considered as representative of the purely transient population plus that part of the working or day population which is employed in Chicago, largely in the area to be served by the West side plant, and which lives outside of the area served by the Sani- tary District. It necessarily is a more or less approximate figure, but is probably as accurate as can be reasonably determined. Some allowance obviously must be made in a city such as Chicago to care for this sewage load contributed to the total by those not enumerated in the Chicago census figures. The quantity of sewage to be treated at each of the five major plants has been estimated from a study of the population tributary to each, and has been estimated upon two bases, viz. (a) under the present system of metering, and (b) universal metering of the water supply. The greater part of the population residing within the Chicago

Sanitary District receives its water supply from the City of Chicago. The total pumpage of the Chicago Water Works for the year 1923, averaged 807,000,000 gallons daily, which the Chicago Water Depart- ment estimates as having been supplied to 3,062,532 people, of which approximately 150,000 were outside of the city of Chicago but within the Chicago Sanitary District limits. In addition to the pumpage by the Chicago Water Department, some water reaches the sewers from private water supplies developed by industries and from the supplies of suburban cities within the area of the Sanitary District of Chicago. There are a few industries developing considerable supplies, notably those in the Stockyards and Corn Products districts.

There is also a small population supplied from municipal supplies within the Sanitary District other than the City of Chicago, the largest of which is the Evanston supply. Others are those at LaGrange, River Forest, Forest Park, Summit, etc. While we have no data as to the total amount of water pumped by industries and municipalities other than Chicago, within the Chicago Sanitary District, it is believed that in total amount it does not exceed five percent of the water pumped by 116 the City of Chicago. Most of the water pumped, in addition to that pumped by the City of Chicago, is furnished under metered conditions, with waste well restricted.

The total population of the cities and villages in the Sanitary Dis- trict (excluding Chicago) has increased from 89,703 in 1900 to 276,930 in 1920. Based upon an average use of 100 gallons per day, the total water used by these villages would be about 30,000,000 gallons per day at the present time, or about four percent of the average daily pumpage of Chicago. The industries probably use enough well water to raise the total to approximately five percent of the Chicago pumpage. Table 5 shows the population of each of the cities and villages in the Sanitary District.

Infiltration of ground water into the sewers is quite indeterminate in amount. The Sanitary District of Chicago has substantially no figures which would furnish reliable information to be used as a basis for the amount of infiltration into the sewers of the various sections of the city under varying soil conditions. No measurements are recorded by the city. Such data as are available are fragmentary only.

The city of Chicago has designed its pumping stations on the basis of 100 gallons per acre per day infiltration in clay soils and 1000 gallons per acre per day in sandy soils. City sewer sizes are determined by flood flows. The greater part of the city of Chicago has a dense clay soil, through which infiltration into the sewers is low. A comparatively small area is sandy. The Sanitary District of Chicago has made its preliminary design of the West Side intercepters, using an infiltration allowance of approximately 2000 gallons per acre per day. The average flow, which is the governing consideration in sewage disposal plant design, is very much less than this amount. It is believed that, taken as an average over the entire Sanitary District area, the infiltration of ground water into the sewers is very small in amount. In th€ computations hereinafter made in Part IX, the infiltration has been based upon 750 G. Po D. per acre which results in the infiltration about one-sixth of the domestic flow or six percent of the total flow estimated for the West Side intercepter.

A part of the water supply never reaches the sewers. It is used for sprinkling and other uses which do not contribute to the sewage flow. The amount of water lost in this way is alos indeterminate. Taken as a general average under the conditions prevailing here in

Chicago, it is probable that if the infiltration of ground water into the sewers is considered equal to that part of the supply which does not reach the sewers, the result will be not far from correct. This has been .

117 the basis upon which the size of the sewage disposal plants outlined in this report has been predicted. We have prepared a table based upon the estimated population and the water use under universally metered and unmetered conditions, showing the amount of sewage which it will be necessary to treat at each of the five major plants for each five year interval from the present to 1945. The last line of this table shows the sewage flow per capita for the entire Sanitary District. It will be noted that, under metering, the total amount of sewage averages from 170 to 171 gallons per capita per day as compared to the water consumption previously estimated herein at 160 gallons per capita per day under completely metered conditions. The discrepancy is due to the fact that in estimating the quantity of sewage reaching the West Side plant, there has arbitrarily been added the flow originating from the 300,000 floating population in that area.

So far as the West Side plant alone is concerned, the basis is believed to be the correct procedure. It is also correct insofar as this floating population represents the population originating outside the boundaries of the Sanitary District of Chicago. Insofar as it includes the population originating within the Sanitary District of Chicago, and simply transferred during the working hours from the area tributary to one of the other major sewage disposal plants to the West Side plant area, it results in an over-estimate of the quantities taking the city as a whole.

TABLE 28. QUANTITIES OF SEWAGE TO BE TREATED UNDER UNIVERSAL METERING AND PRESENT METERING OF WATER SUPPLY.

Plant 1925 1930 1935 1940 1945 Million Gallons Sewage Daily (a) (b) (a) (b) (a) (b) (a) (b) (a)

Des Plaines . 5 6 6 8 8 9 9 10 10 Calumet 53 50 67 41 83 46 102 51 118

North Side . . 193 176 240 145 297 163 354 180 416 West Side 370 316 429 286 485 296 542 306 595 4- 114 S. W. Side.... 256 229 312 182 370 197 430 222 490

Totals 877 777 1054 662 1243 711 1437 769 1629 (1743) Ave. G.P.D. per cap 262 219 296 171 322 170 344 171 364 (390)

(a) Present system of metering. (b) Universal metering. 118

This allowance is, however, in the nature of a factor of safety insofar as it is affected by the shifting of populations from one plant to the other. If half the loop is assumed as originating within the Sanitary

District boundaries, this allowance for the West Side plant is equivalent to including an allowance of approximately 150 gallons per acre per day for infiltration.

Table 28 is a summarization of the quantities of sewage flow to be expected at each of the five major plants under universal metering and under present conditions of metering of the water supply from 1925 to 1945. 119

PART X. FUTURE INTERCEPTING SEWER CONSTRUCTION.

At the present time there are approximately 150 sewer outlets emptying into the Chicago River and the Drainage Canal. The outlets on the North Branch as far south as Fullerton Avenue are all to be intercepted by the North side intercepting sewers for which contracts have already been let. These intercepters serve the North Side treatment works. The present outlets from Fullerton Ave. South and West along the river and main Drainage Canal as far as the village of Sum- mit, are yet to be intercepted and the dry weather flow carried to the proposed West and Southwest Side disposal plants to be located in the vicinity of Summit. All but about thirty-five miles of the total length of intercepters required have already been built. Of this thirty-five miles, twenty miles will be required to collect the sewage and carry it to the West Side plant and fifteen miles will be required for the Southwest Side plant.

Basis of Intercepter Design:

A glance at the map, Figure 3, shows the routes of the proposed West and Southwest Side intercepting sewers. In general they parallel the river and the Drainage Canal, extending along both sides of these channels from Fullerton Ave. on the North Side, southerly to the main channel where they are joined by intercepters laid from the lake westerly, thence through the highly congested central district and along the Drainage Canal to the vicinity of Summit.

In most of this length the congestion is such as to almost preclude open cut methods of construction. The Sanitary District has accordingly adopted tunnel methods of construction, for which the heavy clay soil of this district is admirably adapted. The tunnels are in general at shallow depths below the street surface. Other cities such as Milwaukee, Detroit and Cleveland are using tunnel rather than open cut methods quite largely. On paved streets in

Milwaukee it has been found economical to use tunnels in constructing pipe sewers as small as ten inches or twelve inches in diameter. With the conditions prevailing in Chicago, the adoption of tunnel- ing rather than open cut methods will probably be economical, and will greatly reduce inconvenience to the public. 120

The Chicago Sanitary District has tentative designs for the West and Southwest Side intercepting sewers, the results of which have been furnished to us for our study. An analysis of the design of the West Side intercepters serving about 1,350,000 resident and 300,000 loop or transient population has been made. In general the analysis shows that approximately 143 gallons per capita per day has been allowed for domestic water supply (including the transient use as domestic) an average of approximately 2,050 gallons per acre per day (equivalent to 34 gallons per capita per day 1960 population) has been allowed for infiltration and an additional allowance for industrial water uses, amounting to approximately the equivalent of 120 gallons per capita per day. All of these units are based upon the sum of fixed and transient populations. The total water reaching the sewers under average conditions is, therefore, 300 gallons per capita per day under this design. This amount is increased by approximately fifty percent giving a peak rate flow of 450 gallons per capita per day, which is then further increased by one-third in order to provide for one- fourth of the sewer capacity always being available for ventilation. The sewers as tentatively designed by the Sanitary Dis- trict are, therefore, laid out on a basis equivalent to 600 gallons per capita for the 1960 population.

It is believed that this total allowance, while it includes a larger allowance for ground water than we would consider necessary for Chi- cago conditions, is in the aggregate approximately correct as representative of the conditions of flow in the intercepting sewers if the Chicago water supply is to remain unmetered. It has previously been shown that if meters are not installed the per capita use in 1960 will approximate

440 gallons per capita per day. If this is increased by thirty-five percent to care for peak flows (i. e. 150 gallons per capita per day which is fifty percent of the 300 gallons per capita per day used by the Dis- trict). The total of 600 G. P. D. per capita used by the Sanitary Dis- trict would result. The Sanitary District design, therefore, would not allow any excess capacity for ventilation in 1960, if meters are not adopted.

It is, however, inconceivable that the Chicago water supply will remain unmetered another thirty-five years. It is not believed to be good economic engineering to design long lived structures, such as intercepters for populations expected thirty-five years in the- future and under the worst possible conditions of water waste. The necessity for metering is so urgent and the benefits from it so great that it is in our opinion decidely unwarranted to base intercepting sewer designs upon a continuation of impossible water uses. Universal metering will : :

121 effect a reduction in use per capita for the anticipated 1960 conditions of approximately 280 gallons per capita per day which amount in our opinion may be safely deducted in computing the required capacity of the intercepting sewer system. In other words, an intercepting sewer designed on the basis of 320 gallons per capita per day with universal metering will be fully as adequate as the sewers designed without metering on a basis of 600 gallons per capita per day, the figure used by the Chicago Sanitary District.

Basis of Design: In Computing the capacity required for the West Side intercepters we have adopted the following bases (a) Population tributary 1,370,389 (furnished from Sanitary Dis- trict figures), floating or transient population in loop 300,000 people. (b) Domestic water use 75 gallons per capita per day of resident and floating population. (c) Infiltration at the average rate of 750 gallons per acre per day. (d) Industrial use, as estimated by the Chicago Sanitary District, with the exception of the loop population, the sewage of which we have considered as domestic. The total average sewage flow from this district for 1960 is thus estimated as

(a) Domestic flow 125 MGD. equivalent to 75 GPD. per capita (b) Infiltration 21 MGD. equivalent to 12>^ GPD. per capita (c) Industrial uses 204 MGD. equivalent to 122 GPD. per capita

Total 350 MGD. equivalent to 2091/2 GPD. per capita

Adding to this average flow approximately forty-five percent (90 G.P.D. per cap) for the excess peak rate and allowing sewer capacity sufficient to provide one-third additional for ventilation, a total design capacity of 375 gallons per capita per day is secured. With the above as a basis, the intercepting sewers for the West and Southwest treatment plants have been tentatively laid out. The West Side intercepter includes approximately twenty-one miles of sewers, varying in size from seven feet to seventeen feet. The Southwest Side intercepter has a total length of approximately fifteen miles, varying in size from four feet to fourteen feet three inches in diameter.

The routes of the intercepters are as tentatively laid out by the

Sanitary District and are substantially as shown on Figure 3. The in- 122 vert elevations at the disposal plants will be approximately thirty feet below lake level.

Intercepting Sewer Costs:

In view of the large expenditures involved in the construction of intercepting sewers yet to be built we have thought it advisable to ascertain the facts relative to the costs of building intercepting sewers in other large cities of the country. We have accordingly made investigations of the cost of sewer construction in Milwaukee, Detroit, Phila- delphi, Cleveland and St. Louis. All of these places have been visited and the facts relative to costs, labor conditions, difficulties encountered in construction and other facts having a bearing upon and being necessary to an adequate interpretation of costs were secured. It was found that a large mileage of sewers up to fourteen feet in diameter have been constructed within recent years under contracts relative to which it was possible to secure complete information. An analysis of all of the recent contract lettings in all of these cities was made, and the data thus secured is shown in Figure 20. Inasmuch as the construction of these sewers extended over the past period of approximately five years in most cases, during which time there have been rather violent fluctuations in labor and material costs, the costs in each particular instance have been reduced to present day equivalent costs in the cities in which these contracts were executed. Further correction was then made in order to give adequate consideration to the relation of costs in these other cities to costs in Chicago. These adjustments were made on the basis of the labor scales prevailing in other cities and in Chicago, and upon the proportions of labor and materials entering into the several types of construction and sizes of sewers. These adjusted costs are shown in Figure 21.

Variation in Conditions:

The soil conditions in the various cities and under the large number of contracts analyzed varied quite materially. We endeavored to ascertain the facts in all cases in order that we might interpret the cost data secured.

Of the several sewer contracts executed on the Cleveland intercepting sewers, only three were constructed under conditions similar to those prevailing in Chicago through the district yet to be served with intercepters. Four of the sewers were constructed in whole or in part in quicksand or in wet soil conditions which made the use of air necessary. In our application to Chicago conditions these sewers were eliminated. —

123

3oo —! n inn pn m^Kowina

CONSTRUCTIOM CO^TS OF » - INTU^4NEL- ATT Ac-TUAU ! Pr\ceis Pa\d \- To Accomponq R.epor-4- o-P • \ AuVOR.D.6uT^DlC<.8cHoWSON EnGinieerS Ch\ca<3^o APR.ii_. \925 - t

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Figure 20.—Construction costs of sewers in tunnel, at actual prices paid. 124

Diagram showing Construction Costs or "DEVAjELR-b iisTuhhELL- Adjusted to 275 Chicago 1925 Basis

To Accompanij Rcpor+ o-P Alvord. Burdick ^ HOWSON 250 E.M<2>\»SEIE1RS Chicago Apcil 1925

225

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A Octro i -I- * Mitwaukee-work done wi-fh air Q Cleveland Nofc Thfcse. irKlutk Inanhole^. & Miace

5 10 Diameter in Teeit

Figure 21.—Construction costs of sewers in tunnel, adjusted to Chicago 1925 basis. 125

At Detroit it was found that the conditions of excavation more closely resembled those in Chicago than in any of the. other cities visited. The Detroit conditions are, therefore, peculiarly comparable, so far as costs are concerned. Detroit has also been very active in sewer construction work. Over fifty contracts covering sewers from twelve inches to fourteen feet in diameter have been executed in the past three years. Tunnel work has been done on sizes twenty-four inches and larger. Analysis of Detroit's bids shows good competition to have been secured in which many of the best sewer contractors of the country participated. The range of prices bid indicates that the work is being done under conditions which secure good work at reasonable costs. The Detroit contracts are platted on Figure 20 which indicates the uniformity of prices secured on the Detroit contracts. At Milwaukee considerable intercepting construction has been executed in the past five or six years. Much of this work was in wet sand and much of it necessitated the use of compressed air with attendant higher costs. The Milwaukee sew^er bids analyzed covered sizes from twelve inches to nine feet. Good competition was secured on contracts and considering the difficult conditions of excavation found on most of the work the costs are reasonable and consistent. In addition to making the comparative study of sewer costs in other cities, we personally investigated the conditions under which the

North Side intercepters are now being built, and prepare 1 independent estimates of the fair cost of doing work of that type. The estimates made in this way independently check very well with the actual cost in other cities adjusted for Chicago 1925 conditions. The results of the investigations in other cities and our estimates of the reasonable cost of intercepters are shown graphically on Figure 21. Upon this diagram we have also shown by solid dots the cost of five North Side intercepter contracts, let within the last year or two. It will be noted that these contract costs by the Sanitary District are more than double the prices at which other cities were able to let contracts with prices adjusted to Chicago conditions. The Chicago prices are in many instances practically three times the costs at which the work was let in such cities as Detroit and Milwaukee. Our estimates agree closely with the Sanitary District's estimates for future large sewers. The excavation conditions in most sections of Chicago are at least as favorable as in any city studied. Our estimates assume conditions for the central district and the West Side, about the same as conditions -encountered in the North Side intercepters now under construction. 126

Estimated Cost of West and Southzvest Intercepting Sewers:

Using as a basis the full curved line, showing the cost of sewers of various sizes shown on Figure 21, the use of which assumes that it is possible to build intercepters in Chicago under conditions of efficiency and cost comparable to those obtained in other large American municipalities (adjusted for labor and material cost variations), we estimate the cost of the West side intercepting sewers, including ten percent for engineering and contingencies as $7,890,600. Similarly we estimate the cost of the intercepting sewers for the Southwest plant at $4,495,700. Based upon the Chicago Sanitary District engineer's design as to diameter, which is based upon continuation of the present metering policy, and upon the unit prices herein developed, the cost would be $10,996,100 for the West side sewers and $6,539,500 for the Southwest Side intercepter. Had the estimates been computed using the contract costs on intercepting sewers recently let by the Sanitary District of Chicago, applied to the same sewer quantities as in the first and second paragraphs of this section, the totals would have been approximately $18,210,300 for the West Side and $10,895,500 for the Southwest Side plants respectively, both figures being more than double what are believed to be fair prices for this work.

Period Covered by Design:

The intercepting sewers as laid out herein contemplate 1960 conditions and as stated have a designed capacity equivalent to 375 gallons per capita as of that date, or from 450 to 500 gallons per capita as applied to present population.

The period for which intercepters should be designed is dependent upon a com.parison of the costs and practicability of providing capacity at present for far distant needs and the same facts relative to providing the additional capacity at such time in the future as the necessity occuri,. With sewers built in open cut the cost of duplication usually becomes excessive due to a more complete utilization of the streets by utilities and the increasing difficulties due to community growth and congestion. Such sewers are usually built for long periods in the future. Where intercepters are built in tunnels, somewhat different conditions prevail. Additional sewers can be built in tunnel at a later date with little more difficulty and cost than experienced in the original construction. With sewers in tunnel the period covered by the design accordingly depends quite largely upon a financial comparison of building for ultimate needs or of building for a shorter period with additional capacity added later as needed. :

127

We have made a financial comparison of the costs of intercepting sewers for the West and Southwest Side plants on two bases, both of which assume that by 1960 it will be necessary to double the capacity now to be provided. In one case we have assumed that the sewer now to be built will be constructed at its ultimate capacity, that is, twice what would be required up to 1960. In the second case we have assumed the sewer to be built now as required for 1960 conditions and that in

1960 a duplicate sewer will be built, the cost of which is reduced to present worth and added to the present cost for comparison with the first plan.

The cost comparison is as follows

W. Side S. W. Side (1) Cost of sewer whose capacity is two times that reqd. for 1960 conditions $14,469,400 $ 7,746,200 (2) Cost of sewer for 1960 conditions 7,890,600 4,495,700

(3) Excess cost of (1) over (2) $ 6,578,800 $ 3,250,500

(4) Present worth of cost of duplicating present sewer in 1960 @ 5% 1,430,000 815,000

(5) Saving by postponing construction to 1960 $ 5,148,800 $ 2,435,500

The sewer designed for double the 1960 requirements would be of large diameter reaching twenty-four feet for the West Side plant. The costs used in these estimates are secured from Figure 21 for all sizes up to twenty feet. To secure a unit for sizes above twenty feet a curve of cost per foot of diameter was platted and the unit prices taken therefrom.

Obviously it will be better procedure to design conservatively both with respect to period of time and quantities. Thirty-five years is believed ample provision for time. Quantities should consider metering as being ultimately adopted. We have given consideration to the general routing of sewers proposed by the Sanitary District and are of the opinion that approximately the routes selected will be desirably followed when the detailed surveys and plans are made. We have investigated the practicability of joining the West and Southwest Side intercepters about two and one-half miles above the tentative location of the Southwest Side plant but find that the saving thus effected would probably be less than $100,000. Its practicabiHty therefore is doubtful and can only be definitely ascertained by detailed investigation when the plans are drawn with full information available. 128

PART XI. METHODS OF SEWAGE DISPOSAL AND PRACTICABLE EFFICIENCIES.

Why Sezmge is Treated:

The water-borne wastes of a city are given the general designation of sewage however, in recent years the tendency has been to restrict ; the meaning of the word sewage to those wastes produced by household activities and to designate other water-borne impurities as industrial wastes. In this discussion the word sewage will be used as inclusive of both domestic and industrial water-borne wastes.

Sewage is composed of more than ninety-nine percent of water and less than one percent of soluble, colloidal, and solid constituents. These latter constitutents, in turn, are partly inert or stable and partly organic or unstable. The unstable constituents of sewage are those which create sight and smell nuisances in overtaxed watercourses, and these unstable constituents may be rendered partially or wholly innocuous or inert by subjecting them to proper processes of treatment.

The destruction of the unstable constituents of sewage is a bacterial function which may be carried out in a watercourse or in treatment works in which satisfactory conditions are provided for bacterial activity. The processes by which unstable sewage constituents are destroyed in a stream are the same as those which result in their destruction in treatment works. An important condition governing the bacterial destruction of sewage is that of oxygen supply, and in general, it may be said that in the presence of an ample supply of oxygen the process of destruction will proceed to completion in an inoffensive manner, and that in the absence of an ample supply of oxygen, the process of destruction will result in the production of offensive odors. In other words, aerobic conditions favor inoffensive destruction, whereas anaerobic conditions favor offensive destruction.

A somewhat analogous comparison is that of the operation of a steam boiler plant. When the furnace is properly operated, no smoke comes from the attack, but when the air supply is not properly adjusted, large volumes of smoke or unburned carbon come from the stack. A proper adjustment of the operation of the furnace eliminates the smoke 129 nuisance, whereas an ample supply of oxygen will go far toward eliminating the smell nuisance in the bacterial destruction of sewage.

Hozv Seivage is Treated: The various agencies involved in the treatment of sewage may in a general way be classified as physical, chemical, bacteriological, and biological, none of which alone would suffice. The physical agencies are those of screening, sedimentation, aeration, diffusion, filtration, evapor- ation, etc. The chemical agencies are those involved in coagulation, sterilization, and in the mineralization of certain nitrified products. The bacteriological agencies are those in which the various species of bacteria are the active agents in putrefaction, fermentation, nitrification, and denitrification. The biological agencies are those in which low forms of animal and vegetable life destroy certain constituents of the sewage. In the various methods of sewage treatment in use today practically all of the above agencies are involved to a greater or less degree. Sew- age treatment methods in use today may be classified, in a general way,

as follows : screening, sedimentation, sludge treatment, oxidation, filtration and sterilization.

Sc?'eening:

As practiced in the United States today, the screening of sewage may be classified on the basis of coarse and fine separation. Coarse screens (two to four inch clear opening) have a negligible value as a purifying process and serve simply to remove coarse, solids which might obstruct passageways of pumps or be unsightly in treatment tanks or in a stream. Screens of this character usually remain in a stationary inclined position in the pathway of the incoming sewage and may be cleaned in position, or lifted for cleaning. Fine screens ordinarily have a clear opening of one-eighth of an inch or less and usually rotate through the sewage stream. Most of them are power-driven and are provided with self-cleaning mechanism. The w^ork accomplished by the fine screen is intermediate between that accomplished by coarse screening and very rapid sedimentation. The fine screen probably accomplishes less in proportion to its first cost and operating cost than do other methods of sewage treatment, except under certain conditions where fine screens are particularly adaptable.

Sedimentation:

The treatment of sewage by sedimentation has for its object the reduction of the strength of the sewage by the removal of the settleable solids. This is accomplished by passing the liquor through tanks at a 130 very low velocity, which condition is conducive to a settling out of a portion of the solid constituents. There are two general types of sedimentation tanks in use today; viz., those with one-story and those with two-stories. The one-story tanks are further divided into three classes, viz., those with large capacity for the sludge deposits which are removed at infrequent intervals, those with small capacity for the sludge deposits which are removed at frequent intervals, and those which are provided with a rotating and scraping mechanism for continuous sludge removal.

In the first type of one-story tank the incoming sewage is constantly in contact with actively decomposing sludge for considerable periods of time, and it becomes infected with the products resulting from the decomposition of the sludge. In this type of tank the sedimentation and sludge digestion functions are not separated. In the second type of one-story tank, the injurious effect of the non-separation of the two functions is greatly reduced by frequent removal of the deposited sludge, while in the third type of one-story tank the separation of these functions is practically complete due- to the con- tinous removal of the deposited solids.

In the two-story type of tank the separation of the two functions is accomplished by having a lower story for sludge reception and digestion and an upper story for sedimentation. The upper and lower stories are so constructed that by an arrangement of sloping bottoms, communi- cating slots, baffles, and gas vents, the deposited solids enter the lower compartment automatically and the digestion process may proceed without interfering with the sedimentation process and without infecting the incoming sewage. The two processes thus proceed harmoniously, but sludge withdrawals must be made at proper intervals. In many of the installations of this type, more or less serious trouble from foaming at the gas vents has been experienced and corrective measures to date have only been partially successful.

Sludge Treatment: Solids removed from sewage by the sedimentation process are usually designated as sludge, which, in composition, consists of from ninety to ninety-eight per cent water, and from two to ten percent of dry solids.

The treatment and final disposal of sludge is one of the most troublesome problems of sewage disposal. As sludge increases in moisture content, the volume produced per million gallons of sewage treated increases very rapidly. If the volume of sludge produced per million gallons of sewage be taken at 1.0 when the moisture content is eighty-five percent, the approximate volumes for higher moisture content would be as follows: For ninety percent sludge 1.5, for ninety-five 131

percent sludge, 3.0, and for ninety-eight percent sludge 7.5 ; consequently those processes of sewage treatment which produce sludge of high moisture content, impose the hurden of a treatment of large bulk per unit of dry solid content. There are four general methods of sludge treatment in use today, viz., 1st, lagooning on land, 2nd, pumping into scows and disposing of it by discharging it into deep water at sea. 3rd, partially dewatering it on specially constructed sand filters, after which it may be used to fill waste places or spread on farm land and plowed in, 4th, partial or complete dewatering by pressing, centrifuging, or drying, after which it may be used as a fertilizer, or for filling in waste places.

The disposal of sludge at sea is obviously a method of limited avail- ability. A high degree of dewatering of sewage sludge through the use of presses, centrifuges, and driers, with the intention of producing a marketable fertilizer, has as yet to be demonstrated as a feasible undertaking. The city of Milwaukee, after a thorough and painstaking study of sludge dewatering processes and the fertilizing value of sludge produced by the activated sludge method of sewage treatment, definitely committed itself to the production of fertilizer sludge and now has a very complete dewatering plant well under construction.

The treatment of sludge by m.ethods Nos. 1 and 3 has been prac- tised most extensively in the United States with varying degrees of suc- cess. The chief difficulty which has attended the use of these methods of sludge treatment has arisen by reason of the fact that inadequate disposal areas have been provided.

Oxidation: There are four methods of sewage treatment which might be termed '"'finishing processes," and which result in varying degrees of stabilization of the soluble, colloidal and solid constituents of the sewage. In each of the four methods of treatment, the several constituents of the sewage are changed from an unstable to a stable condition largely by bacterial activities. The four methods of securing a finishing treatment of sewage are the sand filter, the contact bed, the trickling filter, and activated sludge. These four methods of treatment vary widely in capacity per unit of area, and taking the capacity of the sand filter per acre of area as 1.0, the relative capacities of the other methods of treatment per acre of area are approximately as follows : Contact beds, 7.0, trickling filters 20.0, and activated sludge 150.0.

The sand filter when properly designed, constructed, and operated produces an effluent which is clear and sparkling, practically free of suspended matter, very low in bacterial content, highly nitrified, and with 132 an oxygen demand which is so low as to obviate any dilution requirements in a stream. Treatment of the sewage of the Sanitary District of Chicago by sand filters preceded by clarification in settling tanks would require at the present time not less than 8,000 acres.

The contact bed is an oxidizing device and consists of a square or rectangular tank filled with coarse broken stone or other suitable material of varying depth and operated ordinarily on a fill-and-draw plan.

The effluent from the contact bed is ordinarily not clear or well nitrified, has a comparatively high bacterial count, and an oxygen demand which requires some dilution for stabihty. Not less than 1,200 acres would be required to treat the sewage of the Sanitary District of Chicago fo-r the year 1925, in addition to clarification in settling tanks.

The trickling filter is an oxidizing device similar to the contact bed in' general construction but differing in the method of dosing. The trickling filter is dosed by a system of distribution pipes operated under a head and terminating with open spray nozzles properly located and spaced to give uniform distribution over the entire surface. The sewage is sprayed into the air and falls on the broken stone or other filtering medium through which it trickles to the underdrains which carry it away. The cycle of operation consists of a short dosing period, followed by a short resting period. Trickling filters which are properly designed, constructed and operated will produce effluents having a substantial total bacteria] count, a varying suspended matter content, a marked reduction in oxygen demand, and often with a balanced oxygen relation if the applied sewage is not particularly strong. Not less than 400 acres of sprinkling filters would be required to treat the sewage of the Sani- tary District of Chicago for the year 1925, in addition to a previous clarification in settling tanks.

The activated sludge process is a comparatively recent modification of older processes, and might be termed an accelerated bacterial treatment in water. The only sizable plants of this character in operation in the U. S. today are the two municipal plants at Houston, Texas. The literature describing the results of the experimental studies which have been made of this process is quite voluminous. Experimental plants of this character, which have been operated on both large and small scales, have given very promising results, and enough confidence in the process has arisen to justify its adoption for several very large installations. The principal operations in this method of treatment are coarse screening, grit removal, fine screening, aeration in tanks, sedimentation, sludge reaeration, return of a portion of the activated sludge to the aeration tanks, and treatment and disposal of the excess sludge. . :

133

The final effluents from this method of treatment as produced experimentally and by a small number of municipally operated plants have resembled sand filter effluents with the exception that they have ordinarily not been so completely nitrified. The production of an effluent which will not need dilution falls within the scope of the possibilities of this method of treatment. The degree to which sewage may be rendered stable by this method of treatment is capable of some adjustment. This method of treatment is one in which careful and experienced supervision is especially desirable.

Sterilisation:

It is possible to efifect a removal of from ninety to ninety-five percent of the total number of bacteria in sewage by treatment with a sterilizing agent. The efficacy of sterilization will be governed by the size of dose, the comminution of the solids of the sewage, the distribution of the sterilizing- agent, and the thoroughness and sufficiency of the contact of the sterilizing agent with the sewage. Experience with the sterilization of sewage to date seems to indicate beyond doubt that it can be relied upon only to provide a lessening of the burden of water purification where a contact exists. Sterilization destroys bacteria but effects no marked reduction in the organic load, consequently the steriHzation of sewage has no marked effect on stream dilution requirements.

Prac tical E fficiencies

Fine Screening—Table 29 is a partial list of fine screen installations in the U. S., and an inspection of this table will show that the

TABLE 29. PARTIAL LIST OF FINE SCREENS. Sep. No. Dia. Ins. New York City—Dyckman & 210th Sts 14' 3/64 14' 4/64 Plainfield, N. J 10' 4/64 Rochester, N. Y., Irondequoit Works 12' 24/64 12' 8/64 12' 4/64 Bridgeport, Conn. 22' 1/64 22' 2/64 Long Beach, Cal. 14' 2/64 8' Daytona, Fla. . . 5/64 Indianapolis, Ind. 12 6'd. 8'L. 30 meshes Milwaukee, Wis. 8 8'd. 8'L. 6/64 Chicago, Des Plaines River Plant 1 14' 4/64 :

134 clear openings in the screens vary from three-eighths of an inch to one- sixty-fourth of an inch.

Table 30 shows the removal of total suspended solids by fine screens operating on municipal sewage and on industrial waste. An inspection of this table will show that from eight to thirty-six parts per million of suspended solids have been removed by fine screens from municipal sewage, and 103 parts per million from the strong packingtown waste of Chicago. The sewage which is screened at the New York city plant, located at Dyckman and 210th Streets, is a very fresh sewage (less than thirty minutes old) from a residential area.

The removal of suspended solids by fine screening will be governed by the width of the slots, the rate at which the sewage is passed through the screen, and the concentration and degree of comminution of the soHds of the sewage.

The following results have been reported from the screen installation at the Irondequoit plant of the city of Rochester, New York Year 1918— 6.31 cubic feet screenings per AI. G. Year 1919—6.58 cubic feet screenings per M. G. Year 1920—4.58 cubic feet screenings per M. G.

Sedimentation:

The improvement in the quality of sewage resulting from sedimentation treatment will be governed by the concentration and comminu-

TABLE 30. SHOWING REMOVAL OF TOTAL SUSPENDED SOLIDS BY FINE SCREENS.

Width of slots Suspended Solids Source. in Removed Inches P.P.M % (A) New York City—Dyckman & 210th Sts. 3/64 36 26.3 4/64 20 16.6 (B) Long Beach, California 2/64 28 (C) Milwaukee, Wisconsin 8/64 18 8/64 8 (D) 6/64 9 40 meshes 20 (E) Packinghouse Industrial Waste Tests, 30 meshes 103 18.8

(A) Eng. News-Record, Vol. 84 p. 171, 1920 by C. E. Gregory. (B) Eng. News-Record, Vol. 82, p. 1012, 1919. (O) 6th Report Milwaukee Sew. Com., p. 41. (D) 8th Report Milwaukee Sew. Com., p. 72, 73. (E) Report on Industrial wastes from the Stockyards and Packingtown in Chicago, Vol. 2, ^921, p. 182. 135 tion of the solids of the sewage treated, the detention period in the tanks, and the degree to which stored sludge interferes with the settling process.

Table 31 shows the improvement in sewage effecte 1 by preliminary sedimentation as determined by long and short time tests on fifteen of the largest sewage treatment works in the United States. The efficiency of these plants when based on the removal of total suspended solids varies from twenty-two percent to eighty-six percent, with a general average of fifty-five percent. The Proctor Creek plant at Atlan- ta, Ga., shows a removal of eigthy-six percent, but this result is not typical of plain sedimentation for such a large unit, and is accounted for by the fact that certain industrial wastes in the sewage react in such a way as to produce a chemical precipitation. The average result for sixteen years at Columbus, O., is fifty-five percent, and the average result at Baltimore, Md., for nine years is fifty-six percent. The average re-

sult for five years at Fitchburg, Mass , which is a smaller plant and which treats a fresher sewage, is seventy-three percent. It would therefore seem that a fifty-five percent removal of total suspended solids is a very reasonable expectancy, and that a better removal may be secured where conditions are more favorable. A study of the settleable solids in daily composite samples of sewage collected during the past eight years at Columbus, Ohio, has shown that an average of fifty-one percent of the total suspended solids is settleable in a two-hour period in conical settling glasses. This result, however, only applies to the Columbus sewage. Table 31 also shows the improvement in sewage effected by preliminary sedimentation on the basis of the oxygen demand. The determination of oxygen demand is not a routine test at any of the sewage plants listed in the table, consequently information of this character must be based on short time studies. Oxygen demand results on eleven separate plants show an average improvement of thirty-five percent, with extremes of three percent and sixty-three percent. The longest study along this line has been made at Columbus, Ohio, where oxygen demand tests have been a daily routine for sixteen years and the sixteen- year average improvement by sedimentation is twenty-nine percent.

The Columbus sewage is stale and all of it is pumped, both of which conditions tend to reduce the efficiency of the sedimentation treatment. It is considered that an improvement of thirty-five percent in oxygen demand is a reasonable expectancy where the factors affecting sedimentation are average. 1 :

136

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Sedimentation and Sand Filtration: The treatment of sewage by sedimentation and sand filtration in the

United States today is, with one exception, limited to small municipaH- ties and institutions. Numerous small plants of tliis character are in service today but definite information relative to rates of treatment and operating results is very scarce. The largest sewage sand filter plant in the U. S. today is the municipal plant at Worcester, Mass., where, during the year 1923, 64.7 acres of sand filters were operated at an average daily yield of 55,000 gallons. A portion of the sewage of Worcester is treated by sand filtration by reason of the fact that natural sand areas are available. The average results secured at Worcester, during 1923, by the sand filtration treatment were as follows Reduction in total albuminoid ammonia, 89%. Reduction in total suspended solids, 100%. Reduction in total oxygen consumed, 90%. These average results represent a very high degree of treatment, with probably a negative dilution requirement.

Sedimentation and Sprinkling Filters:

The sprinkling filter, almost without exception, is dosed with clari- fied sewage and the effluent from the filter is often given a final clarification before being discharged into a watercourse. The improvement effected by tanks and sprinkling filters with and without final sedimentation is shown in Table 32. An inspection of this table will show that of the total amount of suspended solids removed by tanks and sprinkling filters, eighty-five percent is removed by the tanks and fifteen percent by the filters. In the reduction of the oxygen demand by tanks and filters, the results in Table 32 show that of the total reduction, forty-five percent comes from the tank treatment and fifty-five percent from the sprinkling filter treatment. If the two Atlanta and the Baltimore results are eliminated, the ratio is for tanks forty percent and for sprinkling filters sixty percent. A further inspection of this table will show that the reduction in oxygen demand in parts per million by tanks, with Baltimore results excluded, will vary, on the basis of average results, from thirty to sixty parts and that the reduction in oxygen demand by sprinkling filters, with the Atlanta results excluded, will vary, on the basis of average results, from seventy to ninety parts. The reduction by combined treatment in tanks, sprinkling filters, and final settling basins, with the Atlanta results excluded, will vary, on the basis of average results, from ninety . .. : :

138 to 135 parts. From a study of the best results obtainable, and as recorded in Table 32, a reasonable expectancy from tanks, sprinkling filters and final settling basins is as follows Removal of total suspended solids, 75% average result. Reduction in oxygen demand, 85% average result. Reduction in oxygen demand in p.p.m., 130 average result. Data relative to the reduction in the number of bacteria by this method of treatment is limited to the total counts which have been made at the Baltimore sewage works for a number of years. Average values for a period of nine years from 1912 to 1920, inclusive, at the Baltimore sewage works are as follows Reduction in the total count on plain agar, 67% Reduction in acid forming bacteria, 90%

TABLE 32. SHOWING IMPROVEMENTS EFFECTED BY TANKS AND SPRINKLING FILTERS WITH AND WITHOUT FINAL SEDIMENTATION.

Sprinklers Location By Tanks By By Basins

Atlanta ...... (B) 37 23 60

Tot ..(B) 70 13 83 Remo Suspen Columbus . ..(B) 55 10 65 of % Fitchburg . ..(A) 79 4 3 86 Lexington . ..(A) 60 16 5 71 Solids Total in Baltimore . ...(A) 56 6 16 78

. . (B) 63 31 94

Tot Atlanta . . . ..(B) 62 31 93 Dem ction

Columbus . ..(B) 25 55 80 f .

Fitchburg . ..(A) 38 49 87 Redu %

Oxygen Lexington . ...(A) 40 49 89 in Baltimore . ..(A) 3 67 10 80

a § Atlanta . . ..(B) 32 16 48 a 1 S ..(B) 39 19 58

.2 Q a Baltimore . ..(A) 4 76 11 91

Columbus . ..(B) 39 87 126

Lexington . ...(A) 57 71 128

o Fitchburg . . . . (A) 59 75 inc. 133

(A) Tanks, sprinkling filters and final settling basins. (B) Tanks, and sprinkling filters. :

139

Sedimentation and Contact Beds: Accurate operating results for tanks and contact beds are very analytical data secured limited : however, in Table 33 are shown the by the U. S. Public Health Service from a ten to twelve days' study of the Alliance, Ohio and Canton, Ohio, sewage w^orks which employ this method of treatment. The average results from these two plants show that the improvement effected by this method of treatmeni" was as follows Reduction in total suspended soHds, 85%. Reduction in oxygen consumed, 71%. Reduction in oxygen demand, 80%. The contact beds of these two plants treat between 600,000 and

700,000 gallons per acre per day, which is about one-third of the volume that can be treated satisfactorily by a sprinkling filter per acre per day.

Activated Sludge:

It is difficult to set a standard of practical efficiency for the activated sludge treatment of sewage without relying considerably on results secured by numerous experimental installations. Little doubt exists today as to the soundness of the principles involved, but some doubt does exist relative to the methods and appliances proposed for carrying out these principles. Machinery plays a greater part in this method of sewage treatment than in any other method in common use; also a very extensive air distribution system must be used, which comprises valves, pipes of many sizes, and in all cases final air outlets which are extremely small. The coefficient of dependability of some features of this process may be said to be somewhat uncertain however, the ; several features of this process have been very carefully investigated by so many competent chemists and engineers and their conclusions have been so well founded that its adoption as a practical method of sewage treatment seems to be based on sound judgment.

In Table 33 will be found analytical data secured from a ten to twelve-day study of the north side and south side plants at Houston, Texas, analytical results secured from a two years' operation of the same plants, analytical results of a ten to eleven-day study of the plants at San Marcos, and Sherman, Texas ; also results of twenty-three months of operation of the Des Plaines River plant of the Sanitary District of Chicago. The Des Plaines plant has been operated on a combined routine and experimental basis, consequently the results are probably not such as might be secured if it had been operated with a single purpose in view. 140

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142

Omitting from consideration the results from the Des Plaines and Sherman, Texas, plants, the results recorded in Table 33 indicate an improvement from this method of treatment as follows Removal of suspended solids, 94%. Reduction in oxygen consumed, 81%. Reduction in oxygen demand, 92%. The north side and south side plants at Houston, Texas, treat approximately six million and one and one-half million gallons per day, respectively. The San Marcos, Texas, plant treats approximately 200,000 gallons of sewage per day. The use of the activated sludge process for the treatment of packing and stockyards sewage has been tested experimentally by the Sani- tary District of Chicago, and the improvement elfected, as based on data recorded on pages 47 and 134 of the Report on Industrial Wastes from the Stockyards and Packingtown in Chicago, Vol. 2, 1921, San.

Dist. of Chicago, is as follows Removal of total suspended solids, 91%. Reduction of oxygen demand, 96%. Reduction of organic nitrogen, 83%.

Warm Weather Efficiencies:

In view of the fact that during warm weather there is an accelera- tion of bacterial activities both in polluted streams and in bacterial processes of sewage treatment, it is evident that dilution requirements in a stream during warm weather are at the maximum, and, for the same reason, it would seem that the efficiency of sewage treatment would be higher wherever bacterial processes are involved. A study of the average monthly efficiencies at the Baltimore works for a period of nine years, the sand filtration treatment at Worcester, Mass., for 1923, and the Columbus works for the year 1913, indicate that the average efficiency for June, July, August and September is above the average efficiency for the year in the following amounts Baltimore, four percent Worcester, three percent Columbus, ; ; three percent. An average efficiency for the warm weather months of the year, of three percent above the average annual efficiency is a reasonable assumption for sand filter, contact bed, sprinkling filter and activated sludge treatment.

Conclusion on Efficiency:

In consideration of treatment works for the largest sewage disposal plant in the world, we believe we are warranted in expecting the best of operating results. We conclude that it will be practicable to 143 secure the following net efficiencies in the proposed Sanitary District plants, in the warm or critical season of the year, expressed in percentage of the biochemical oxygen demand removed from the sewage compared to sew^age as delivered before treatment. Tankage, 35%^. Tanks and Sprinkling Filters, 88%. Activated sludge on Domestic Sewage, 92%. Activated sludge on Stock Yards waste, 95%.

Applicability of Other Means of Sewage Disposal: The subject of sewage disposal for Chicago would not be complete without consideration of certain means for sewage disposal that have been extensively used abroad but which are not considered to be adapted to the local situation at Chicago, particularly when taking into consideration the expenditures that the Sanitary District has already made. We believe it v^^ill be useful, briefly to outline these methods of disposal and to show why it would not be practicable or economical to adopt them.

Broad Irrigation:

The oldest method of sewage purification is the disposal of the sewage upon farm or garden land, commonly called Broad Irrigation. The sewages of Berlin and Paris are thus treated, and the method has been extensively used in Germany, France and England.

Inapplicable to Chicago Conditions: If Broad Irrigation should be adopted for Chicago, about 60,000 acres or ninety-three square miles, would be required under the average rate of application to land as practiced in England, where, in general, available land contains more or less clay. If sandy lands could be found, similar to that available for sewage disposal at Berlin, about 25,000 acres or thirty-nine square miles, would be required. It is believed that no such large areas are available, without carrying the sewage a long distance from Chicago. No surface soils' of a sandy nature are available nearer to Chicago than the east line of Gary, which is approximately forty miles distant from the Chicago loop district. A sufficient area could probably be found east of Gary, but the land is very rough and large expenditures in grading, or in pumping, would be required to make it useful. A sewer about twenty-five feet in diameter would be required to accommodate the present total sewage of the Sanitary District. This sewer would cost about $1,500,000 per mile. Approximate estimates indicate that the initial investment in an outlet sewer and pumping 144 works alone would exceed the cost of the intercepting sewers and the more modern methods of sewage disposal, for which we have previously estimated the costs. In addition it would be necessary to purchase the lands and put them into condition to receive sewage.

Site Below Jolict:

Before the drainage canal was built the suggestion was made to carry the Chicago sewage through a tunnel and dispose of it by gravity upon lands adjacent to the Des Plaines River below Joliet. This might have been possible with the quantities of sewage produced by Chicago thirty or forty years ago. At the present time it would not be possible to. find an acreage sufficiently large to treat the sewage by Broad Irriga- tion, delivering the sewage by gravity flow. Lands m.ight be found to which the sewage could be pumped.

The land at this location is of a sandy and gravelly nature. It would probably be well adapted to sewage farming. Rough estimates indicate that the cost of development, including tunnel and pumping, would not be less than the figures previously given covering sewage farming on the lands east of Gary. Therefore the costs would materially exceed the costs of work§, herein elsewhere estimated.

Broad Irrigation Not Practicable: There are other and more important reasons why broad irrigation would not be applicable.

(a) Sewage farming is viewed with disfavor by American health authorities, as dangerous to public health. (b) Climatic conditions arc much less favorable in this region than in Western Europe by reason of the severe winters.

• (c) The American public is less tolerant of local nuisances than the European public, and is less inclined to properly maintain its sewage works. A sewage farm would be an intolerable nuisance unless well operated.

Other Disposal Methods: We have herein elsewhere mentioned contact beds and sand filters as means for secondary purification, which have been more or less extensively usd by small cities and large public institutions. Either of these methods, by reason of the large areas required, would necessitate large expenditures for intercepting sewers to carry the sewage to more or less distant and remote locations. We believe that the relative areas required, as stated elsewhere in this report, are sufficient to indicate their higher cost as compared to the methods of sewage purification upon which we have prepared detailed estimates. 145

PART XII. SEWAGE DISPOSAL COSTS IN OTHER CITIES.

Chicago, through the Sanitary District, is undertaking a great sewage disposal program. To date, although the second Jargest city in the United States, it has not constructed and operated disposal works of magnitude commensurate with its wastes. Certain other cities have had considerable experience in the construction of sewage disposal works of the types generally considered as applicable to Chicago conditions. The costs of these works, are capable of analysis considered as units, so that knowing the number of units of each plant item required, costs of similar plants in individual cities may be compared. If in this comparison the varying costs of labor and materials are brought to a common basis, the results are quite reliable as an indication of fair costs under the conditions pertaining to that basis.

In order that we might have first hand information as to the costs of construction and operation of the larger sewage disposal plants of the country, and have sufficient familiarity with the plants and their operations to interpret the cost of construction and operations and trans- late them to Chicago conditions, we visited the more important plants, including Baltimore, Cleveland, Philadelphia, Albany, Indianapolis and

Milwaukee. At all of these plants we were courteously extended all of the available information relative to cost of construction and operation. This information has been supplemented by other cost data in our possession. We gave particular attention to the costs of construction and cost of operating: (a) Tankage plants.

(b) Tankage and trickling filters. (c) Activated sludge plants. (d) Pumping Stations. which types of construction must necessarily be included in any comprehensive study of the Chicago situation. We also investigated sewer construction and costs in a great many cities.

Adjustment of Costs to Chicago 1925 Basis: In each of the several cities visited to secure costs of sewer and sewage disposal plant construction the costs of labor were found to vary. :

146

It was also found that the construction studied in the several cities had been executed at different time periods and accordingly under varying price level conditions. In adapting these data for use in studying reasonable Chicago construction costs, it was accordingly necessary to make two adjustments, viz (a) For location. (b) For time.

The first adjustment was made by studying the labor costs for the various types of labor involved in each construction project and ascer- taining the weighted average relation of those costs in the city being studied to those prevailing in Chicago. This resulted in securing a factor wliich applied to the costs in the city studied, would reasonably indicate the costs in Chicago as of the same period. In cities for which there were no printed data available as to labor costs inquiry was either made by letter or the costs prevailing in the nearest city for which the data available were used. Table 34 shows the rates for skilled construction, skilled operating and common labor in a number of cities expressed in percentage of Chicago rates for the same classes of labor.

The comparison is as of 1925. The adjustment for time was made by using the United States Department of Labor data relative to fluctuations in prices for building materials, and the prices paid by the City of Chicago for skilled construction labor, common labor, skilled operating labor and engineering or supervisory services. Figure 22 shows diagrammatically the cost index of building materials from 1913 to 1925, based on United States Department of Labor data. Figure 23 shows the variations in the rates paid by the City of Chicago for various classes of labor entering into the construction and operation of sewers and sewage disposal works. In the application of these data to the various types of construction it was necessary to estimate approximately the percentages of materials and labor and the relative proportions of each class of labor required. All time corrections were computed as of the date of letting contracts. In some cases where several contracts were involved the resulting time factor w'as a weighted composite of the individual contracts. In case of defaulting of the original contractor and the reletting of the work the latter date and contract cost were used for the date and pay- ments under the original contract. / / P —

147

Co=»T \noex op Bu\ud\ng MATC^IAU^)

U. e>. Oh.p>-t of Labor. loiN-bm too %

Figure 22. —Cost index of building materials.

WS.-r*.-r>o»4 OT=^«.Jfc.-r /5\ Sk.\\_\_«.o \_A.e>oH.

=^ 1 \ ^ r—

6, r- 1 i

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!qi4. T^Ts ioTTiqii i^iq ii-zo iqii nrz ii-za 1925

Figure 23.—Variations in skilled and unskilled labor rates in Chicago, based on City of Chicago records, 1913 being 100%. . .

148

TABLE 34. TABLE SHOWING % RATIO OF SALARIES PAID TO SKILLED AND UNSKILLED LABOR IN VARIOUS CITIES, BASED ON CHICAGO PRICES IN 1925 BEING 100%. Common Skilled Labor City Labor Construction Operation

Albany, N. Y 85.0 92.5 87.0 Atlanta, Ga 36.4 78.8 61.8 Baltimore, Md 48.5 96.0 68.0 Boston, Mass 78.8 84.5 85.1 100.0 100.0 100.0 106.0 99.5 103.8

Columbus, Ohio . 48.5 88.4 83.3 Fitchburg, Mass. 60.6 84.1 81.6

Houston, Texas . 48.5 96.6 81.0 Indianapolis, Ind. 54.5 95.9 95.5

Lincoln, Neb. . . 40.0 to.o

Milwaukee, Wis. < Z.b ol.v

Urbana, 111 66.6 92.1 84.0 48.5 73.8 73.8 66.6 87.8 70.0 66.6 87.8 70.0 Detroit, 72.8 93.5 95.0 106.0 116.0 102.7 64.6 87.0 76.8

Tankage Plants:

The largest tankage plants of the country, which at the present time are operating without secondary treatment, are those of Cleveland (Westerly Plant), Rochester, (Irondequoit Plant), Philadelphia and Albany. In each of these plants we ascertained the facts relative to first costs, date of construction, and the costs of operation. The data relative to construction costs are shown on Table 35. Inasmuch as these costs were incurred during a period of rapid and great fluctuations in prices, all of these costs have been reduced to the basis of 1925 conditions, and then further adjusted for the difference in conditions prevailing in -each of these towns as compared to Chicago. ~ The costs reduced to the 1925 Chicago basis average $5.00 per capita and $30,750 per million gallons daily capacity. At the bottom of this table are shown similar figures for the Calu- met plant of the Sanitary District of Chicago. The per capita cost of 149

the Calumet plant is $26.40 and the cost per M.G.D. capacity is $86,000. The tabulation of bids on the Calumet plant shows that the concrete for the tanks, 28,000 cubic yards, was let at a price of $64.00 per cubic yard exclusive of reinforcing steel. The steel, 3,000,000 pounds, was let at a unit price of twenty-three cents per pound. The concrete complete, therefore, was let at a unit price exceeding $85.00 per cubic yard. The. work included thirty tanks permitting multiple use of forms and plant. In making the comparison of construction costs for utilization in

preparing estimates for Chicago plants yet to be built, all figures w^ere reduced insofar as possible to a unit volume or capacity basis. On tank-

age plants for example the comparison is based upon the displacement

TABLE 35.

CONSTRUCTION COSTS OF TANKAGE PLANTS (2 Story Type) INCLUDING SCREENING, GRIT CHAMBERS AND SLUDGE DISPOSAL.

• MGD

for de-

ruction rsion Ition Built for Led ity L Construction Costs Based on Chicago Quant Actual L/Onsil signed Conve Facto: a'm Year Cost Prices of Material O

*Corrected for 1 M. G. D. activated sludge and 4.44 acre ft. of filters and for land. **No sludge drying beds—Cost adjusted on basis of 1919. (a One-third built under original contract—two thirds under new contract let in July, 1920. No Intercepters or Pumping Stations included.

volume of both the flow and digestion chambers in order to eliminate the variations in detention periods, sludge storage per capita, strength and amount of sev^age and the momentary under or overbuilt condition of the plant. The average and weighted average of the costs for each part of the plants, such as screens, grit chambers, tanks, sludge beds, etc., were secured for use in estimating reasonable construction costs for Chicago conditions. The detailed data are shown in Table 38. . ;

150

Weighted averages were computed in order that the relative effect of size of units upon cost might be taken into consideration.

Table 36 shows the operating costs of these Imhoff tank plants. It shows also the cost of operating the separate digestion tanks at Balti- more in which the operating costs are excellently sub-divided so that the ,tank and sludge operations are available. We have also shown the facts relative to the Calumet plant of the Chicago Sanitary District on this table.

TABLE 36. OPERATING COSTS OF TANKAGE PLANTS.

Liting ion dbo o. Operating Costs re- Co duced to Chicago 1925 pulat ntribi eated nual erati] avers iered ctor ar sts asis — Labor Only o o c o a O 03 Changed per per City Total Total" Capita M.G.

Cleveland 1924 87,000 4,800 $ 33,847 0.975 $ 32,929 $ .378 $6.85 Rochester .... 1919 240,000 12,050 30,809 1.48 45,625 .190 3.78

'Philadelphia .. 1924 117,000 8,100 28,420 1.31 37,280 .319 4.61 Albany 1920 104,358 5,220 21,127 1.29 27,202 .261 5.21 Baltimore .... 1923 690,000 20,100 75,842 1.07 81,352 .135 4.04 Average .256 4.90 Weighted Ave. .192 4.47 Calumet, Chicago Sanitary Dist. 1924 90,000 10,600t $199,567t $199,567t $2.22 $18.82

*No sludge drying beds—sludge pumped to Lake Erie. **No sludge drawn to beds in 1924. tDeducted 1180 M. G. estimated sljidge operation @ $21.95 = $25,800.

At the Westerly Cleveland plant the sludge instead of being dried

on beds is discharged into the outlet sewer. The total operating ex-

penses of this plant were credited with the cost of chlorination which is practiced during the summer season.

At Philadelphia the plant is provided with sand sludge drying beds but no sludge was removed during 1924. Baltimore, a separate sludge digestion type of plant, has the lowest per capita expenditure for tank and sludge bed treatment of any of the large plants studied. It will be noticed that the weighted average cost of operating Im- hoff tank plants adjusted to Chicago 1925 conditions was 19.2 cents per capita and $4.47 per million gallons treated. The Calumet plant in Chicago, built in 1920, with costs adjusted for a small experimental plant and reduced to 1925 conditions on the same basis as the other 151 plants was $2.22 per capita and $18.82 per million gallons. The per capita cost was ten times the average of the other plants, and the cost per M. G., due to the higher per capita use, was still over four times the average and nearly three times the highest of the other plants. Comparative cost of construction of these plants is shown diagrammatically on Figure 24. The operating costs of Tankage plants in cities other than Chicago vary from 13.5 cents to nearly 38 cents per capita, adjusted to the

HecivL3 linee indicafe 1000 DoUart> per M.G.D LiQh'i • - Dollars perCapifa UnisHoded cir-

Plants

Figure 24.—Cost of constructing Imhoff tank disposal plants, based on 1925 Chicago conditions. 152

Chicago 1925 basis and from $3.78 to $6.85 per million gallons treated referred to the Chicago 1925 price basis. These facts relative to operating costs, together with the operating cost of the Calumet plant of the Chicago vSanitary District are shown diagrammatically on Figure 25.

Opcra+ion Maw^dnanca. - Dollars per Million Gallons.

O cn 5 ui o

ROCHESTCR

Balximorc.

Philaoc.i_p>mia

No sludqe rzrr\o^e.c

ho eludgc beds

Crediteci With rr-ioU Ac+ivated Sluolg«Plan+ Operation

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Opero+ion Sk W\Q\r\\Q,rtariCC- Dollars per Cap! fa

Figure 25.—Cost of operating tank disposal plants, based on 1925 Chicago conditions.

Heavy lines indicate $ per million gallons. Light lines indicate $ per capita.

Imhoif Tank^ Sprinkling Filter Plants:

In a manner similar to that just outlined we investigates! the costs of construction and operation of eight (8) Imhoff tank sprinkling filter plants, all cost being reduced to the 1925 Chicago basis. Insofar as possible the costs of construction of these plants were likewise subdivided into the various units of the plants, such as screens, grit chambers, settling tanks, digestion tanks or digestion compartments sprinkling filters, secondary tanks, sludge beds, etc. These costs were 153 further reduced to the cost per unit of capacity, either per capita, per million gallons or unit of organic load, so that insofar as possible the unit prices thus secured might be available for use in estimates for Chicago costs. The comparison of the unit construction costs of these plants is shown on Table 35 hereinbefore referred to under Imhoff Tanks. On Table 37 we have shown the summarized costs of the sprinkling filter plants taken as a whole, without respect to the variations in design periods, rates, etc. These costs while more general than those secured from the analysis of the several parts of each plant nevertheless are of interest in showing the average costs of complete plants under widely varying designs. An estimate for any particular set of design conditions can be prepared by applying the unit costs set forth in Table 38 to the corresponding units determined upon. A study of the operating costs of the tank-sprinkhng filter plants was also made, the results of which are shown on Table 39. This table shows contributing population,, million gallons treated during the year, the actual operating costs furnished us, these costs reduced to Chicago 1925 conditions and expressed in total, per capita, and per million gallons. All of these plants are complete and the costs of operation include all such items as labor on coarse screens and grit chambers, labor and power on fine screens at Baltimore (the only plant in this number having fine screens) sludge handling, sludge drying, cleaning of sprinkler nozzles, operation of laboratory, superintendence, maintenance and repairs. The detailed costs under each of these subheads are not available for the several plants in comparable form and are accordingly omitted herein. It will be noted that the weighted average cost of operating tank sprinkling filter plants was 26.1c per capita or $8.82 per million gallons treated, based on Chicago 1925 conditions.

Activated Sludge Plants:

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